So I've decided to make another post on here. I need advice with a lot of things apparently. This one is the most important to me though, because there could be problems in the future involving Koda and my other animals.

I have a small Shih Tzu/Maltese mix named Lola. Since the day we got Koda, he's been much bigger than her. I also have 2 cats, one of them knows how to run away and the other is a smaller kitten who sits in one spot and hisses.

Koda gets way too excited with my other animals, especially Lola. The second he sees her he tries to lunge at her/chase her and pounce on her back, and no matter how much she runs or screams/growls/cries, he is way too overwhelming and because of her size and breed I'm scared that he's going to hurt her by pouncing on her. That, or she finally decides to attack him and if he attacks back someone is getting hurt really badly. I've tried introducing them with him on a leash, or behind gates, but in the end when he knows that nobody is there to restrain him he is uncontrollable and does not listen to the commands i've taught him.

With the cats, they run away or stand their ground and hiss at him. He still tries to harass them relentlessly and has gotten scratched in the face a few times.

I don't know how to make him leave them alone. I have to keep him behind gates and separate from all of the animals every single day and rotate them in between rooms. I don't know what I'll do when he gets too big and is somehow able to get over the gates.

The big issue is the energy level. Koda is a puppy and a tired puppy is a good puppy. And you may have to work on crate training and try walking the dogs together. I think you may be expecting too much too quickly. Please dont take this the wrong way but is your small dog trained or did you go the its a little dog and cute and not treated like a dog route. Because you cant go well its just a little dog.... then turn around and expect koda to behave because of his size. I know lots of people with big and small dogs and usually the small one ends up running the show. Also is koda neutered? I would keep him separate unless you are there and ready to step in and stop it the instant it starts to reinforce that the behavior is unacceptable

He's calmer around the cats when tired but still as energetic with her when half asleep. I've tried walking them together but my mom freaks out because he tries to chase her and jumps in the air and the leash snaps him back so my mom doesn't like that.

I'm not sure what you mean with the question about Lola though, she doesn't know commands but she is very smart. She is absolutely terrified of Koda and won't go near him.

Koda is not neutered yet. We're able to neuter him in about 2 weeks.

I have kept them separate for a while and haven't tried to introduce them again. They sniff each other through the gates and seem like friends through the gate, but I know when I let him loose with her it will be the same. I can't keep him behind the gates forever though. I've had him for almost 2 months and no progress yet

Your puppy is still young and should not have so much freedom. I would keep s leash on him at all times unless he's crated. Keep him either tethered to you, something sturdy or in the crate. You can also let him drag leash around while you are there so you can grab the leash and pull him back from whatever mischief he's into at the moment. Having a puppy is an 18 month exercise in full time parenting. This is the time for training and socialization. With the leash dragging, you are able to teach him "no" and to when called.

I echo what @amymeme said but I'll also add what worked for me.

You can't expect that the dogs and cats will get along quickly or all the time so they all need someplace where they can be safe. When I introduced two kittens into my household of three adult dogs ( the reverse of what you have ) I gave the kittens the back part of my house (it's a house trailer) and I and the dogs lived in the front half with a gate like this. The kittens could walk through the gate but the dogs couldn't (and wouldn't jump it, though two out of the three could have) so eventually the kittens migrated into the rest of the house and since the dogs knew who they were they didn't bother them (much and that's playful.)

If I were you, I'd "isolate" Koda beyond a gate. He gets to be part of the family when he behaves and when he doesn't he either gets crated or put in his isolation chamber. What is important in this exercise is the the various animals have the ability to see and smell each other - they have to realize (and they will) that they're all a part of the same home.

I'm thinking that the excitement level when he does get to be around the other pets is a major part of the problem ... by being able to see / smell them while still being separated from them it should reduce the level of excitement.