I would try my best to make it short.
Recently a friend of a friend has to give up the ownership of a year old male husky. That's catch my eye as I feels sorry that such amazing character, well behaved husky has to come across with this. Thus, my partner and I took him-Simba home, but instantly my current 5 yo male husky- Charcoal does not like him and almost both get into a fight. Simba has been with us for 3 days but I can tell Charcoal is real upset and I feel psychological exhaust to keep on eye to prevent fight and keeps both happy. They would get into argument of all sort of things, as simple as who gets pet first. Somehow I feel like I betray Charcoal to have other one and or I being cold to ignore the Simba.
I missed the old days when Charcoal closed to me.
Am I ready for new joiner?
How long does it takes for the transition?

I think it's great what you're trying to do for Simba. Is Simba neutered? Is Charcoal neutered?

Adding a new pack member doesn't happen instantaneously. When we adopted Diablo a bit over a year ago, he was being added in to Demon and Dakota who had been together their whole lives. We had quite a few squabbles, especially between Demon and Diablo (some bloodshed). It took almost a year for them to completely settle. We still get Demon putting Diablo in his place, but we haven't had bloodshed in quite a while now. Sometimes you just need to let them settle their own disputes.

You need to ease them into being together, especially if they've never really interacted before. You're bringing someone new into Charcoal's family. You need to show him that everything is ok and that Simba is family. Continue to give Charcoal some one-on-one time in addition to trying to introduce him to Simba. Feed them in separate areas so they don't have the chance to fight over food (for example, Demon and Dakota are fed in the kitchen. Diablo gets his food in his crate, downstairs from the kitchen).

@Demon&Dakota, Thank you for your advise.
They both are boy, so strong dominance does show on both dogs, which is my fault didn't put everything into account carefully.
One dog household pack would be (I unsure am I get this right):
Me-->Charcoal-->Partner(but in a rare case when Charcoal misbehaved, Partner would be the king of the pack to sort thing out)
Now, I am unsure is it a right move and have a little bit concerns for what would be the best or fairest way for everyone in the household. I would be the mainly only person to look after dog(s) because I am currently unemployed, but situation would be change not far in the future. Apart from that, excluded cooking, I would be the only to look after a one bed flat house work. On the other hand, before Simba come, Charcoal seems comfortably stays at home alone after his pal left him more than a year ago.
Thus,
1: Is one bed flat is slightly packed for two dogs and two adults to habitat which would easily flag up fight?
2: What would be the most beneficial for Charcoal, being the only child or having a new pal?
Thank you in advance =)

Two males can get along fine.  Sometimes they just need to work out their differences.  Are both dogs neutered? Sometimes that can cause problems.

You're asking if a one bedroom apartment (flat) will be too crowded with 2 humans and 2 dogs, right?  I don't think so as long as the dogs get adequate exercise.

Huskies are pack animals...most like to be in groups.  There are always going to be some that are the exceptions though.

It sounds like you have the time right now to spend introducing Simba into the family.  The question is, do you really want to?  It takes time and patience.  Make sure each dog has their own space that they can escape to.  Whether it's a crate or a bed or another room.

Regardless of how many dogs you have, you and your partner (the humans) are the bosses.  Both of you should be correcting bad behavior, both of you should be providing food, treats, walks etc.

Do they play together at all?  Do you have a place where they can run around a bit, that is neutral territory?  Since I don't know where you are, I can't say whether there are dog parks or anything else of the sort.  Another option is a behaviorist.  Just see if they can observe the interactions between the 2 dogs and tell you if it's normal for the situation or if there's a problem.  

In the end, you and your partner are the only ones who can determine if the situation will work out.  A few days, in my opinion, isn't enough time to figure out if things will work.

Diablo drove us nuts when we first brought him home.  He wouldn't settle, he constantly wanted to be outside even if he had just come in, he paced, he annoyed the other two to no end.  It took a couple of weeks before he started to settle down in the evenings.  It took until Demon pinned him and drew blood before they settled into a hierarchy.  I think that was a month or two into us having Diablo.  It's scary when that happens, but sometimes they need to do it to establish their place in the pack.  He still tries to challenge that hierarchy at times, but is quickly put in his place.

This picture is about 3 months after bringing Diablo home.  Dakota's not thrilled about sharing her space, but she's tolerating him:
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Here, the boys are cautiously sharing space after about 4 months:


And finally, 8 months after bringing him home, we have peace:
(sorry, not sure how to rotate it)

@Demon&Dakota, Much appreciated for your time and effort to write this up for me, after a week, they are getting on much better than the first few days as I think they have find their state in a pack. But occasionally they do get into argument or fight over food. By the way, the first picture on the left hand side husky (Demon, I guess?), that look is exactly how Charcoal looks when he first met Simba.
YES, I reckon my flat become smaller when Simba comes. Would you recommend I should keep him if I walk them 2 times daily?

I'm glad they're starting to get along better. Arguments are going to happen, just like with kids. Unfortunately I can't make this decision for you. You need to decide if this is something you want to do and if it's the right thing to do for your family.

Can you elaborate on how this fighting over food takes place? What's the scene like?

@Demon&Dakota, I can't express myself to thank you for your support. Thumb up!

@seattlesibe, for example when it is treat time, they are sit side by side and waiting for commend to earn treat, somehow, one start up the argument and quickly might turn into a fight sometimes. Other example, when I am prepare food for them, Simba stays really really close to me and I hardly can claim an area to work. Moreover, most of the time he would howls while I am preparing food. I have tried to stare at him to claims mine but often fail over food.

So how do you respond when one starts a fight? Why are they doing this in the first place, sitting side by side waiting for treats? What are you teaching them or having them do?

Easy fix for Simba guarding you and the food--------Simba is not allowed anywhere near you or the food during feeding. You are training Simba to protect you and the food. You need to set some boundaries here and keep Simba away from you. If he is rushing you and pushing towards you and howling and causing a fight, stop allowing him near you.

When you feed him in this excited, protective, bratty state of mind you are training and reinforcing this behavior. If you want to end the fights and the nonsense:

-have a designated area for each of them to separately wait for food while you are preparing it.
-once the food is prepared, if you hear any howling or talking say No,calmly, and put the food away. Meal time is over.
-once you get them quiet, set the food down. If they leave their area or rush you, put the food away. Meal time is over.
-repeat this every half hour for 2 hours, so try 4 times. If they don't get it, they don't eat that meal at all. It is okay to have them skip a meal. They will learn VERY fast what you want if you leverage their appetite. Once you get the behavior you are looking for, say Good, calmly, and then invite them to come to the food and eat.

You want to wait for patience and calmness prior to feeding. And they must eat separately. This will end the fights.

What Jeff said. It works.

Analogous situation here: When I want to take Ami for a walk, we walk down to within 30 ft of the invisible fence boundary, I want him to sit to remove his fence collar and put on his prong collar and leash. He is so excited for walk that he paces and walks about 10 ft for me, waits for me to join him and then starts pacing again.

Solution? I stopped where I wanted to stop and waited. He looked annoyed. I waited. Without a word. Finally, reluctantly, he turned around, came to me and sat. Works.

Great points Amy.

Basically no words are required to teach a dog boundaries. You can't point to a spot, imply significance to a spot, reinforce a spot, and correct for leaving a spot with the use of no words whatsoever.

Words, for the most part, create excitement and energize dogs--positively or negatively, or create stress and make dogs anxious or fearful. The pick up on the tone of our words and our emotions coming through our words.

It's a lot easier to be neutral without words.

@seattlesibe, thanks for reminding me all the training bit and would give it to try. =)