Archer is 3 months old and recently I noticed that if one of the other dogs comes up to him while he's eating he flips out. There are 4 dogs in my house as opposed to the normal 3. Nikita and Archer are both fed on their crates. Harley, my 9 year old shih tzu mix, is free fed (his bowl is picked up when the "big dogs" are out and put down when they're up or outside). We also have my brother's girlfriend's 10 week old shih tzu, she is given a bunch of feeding times. My brother deals with her. 
Archer is perfectly fine with me being around him while he's eating. I can pet him, put my hand in his bowl, hand feed him, mess with his paws, ears, tail, everything. But when one of our other dogs walks by or sniffs his kennel he barks and tries to guard his bowl. It then spills and gets food everywhere which makes the dog linger to pick up the spilled food. I'd hope to eventually be able to feed Archer and Nikita together and get rid of the crates for the most part. That won't happen until I move out but that's the plan. Is there any way I can nip this in the bud? 

Also, to me he seems skinny, the vet didn't seem worried about his weight though. He's pretty active so I tried to bump up his food intake but any time I tried, his stool would go soft and stay soft for weeks until I bumped it back down. I'm almost done switching his food from what he was on when I got him to what Nikita is on. He's done great with that! Should I try to bump it again after the transition is done? He gets 1 cup in the morning and 1 at night at the moment. He scarfs if down like we never feed him. Could it be that he's not getting enough? So he thinks he has to guard his food from the other dogs?

I handle mine by making the "rude" dogs eat slower than the dog I can trust to leave the others alone. I have one dog who is food aggressive and he's also rude and would like to push the others off their bowls if he gets done early. He eats out of a slow bowl so I don't have to babysit him. The other dogs I would just get onto them when they get done if they get too close to him so he doesn't feel the need to try to guard from them or get worked up. I also fed him further from the others so that they aren't forced too close. Teaching all of them manners is key. Everyone needs their space. The other dogs need to respect his when they get done before him and visa versa. You might could also throw a blanket over his crate so he can't see them wandering around when they are done while he's still eating.

So squirt has her own room and is fed twice a day. Shadow is fed twice a day on one side of the room and his bowl is picked up when hes not eating and spider and splinter share a bowl and are freefed. Shadow has majorly loud hoarding issues that start with the bowl. When its empty and out he then collects all the dog toys and puts them in the bowl and guards the bowl of toys. He is also grumpy and constantly growling at the other dogs to get thier attention.He only does that to the other dogs not me and lately spider has started showing her teeth to shadow when he tries to eat her food. Its kinda funny and really loud. Every once and awhile it goes too far and i have to get involved but aside from not letting shadow eat from spiders bowl and not letting spider steal shadows bowl, i let them work it out. Something ive noticed in my pack is when something is really about to go wrong it gets super quiet so to me the noise is a good sign. And i know with small dogs involved it can go from 0 to 100 in a fraction of a second, splinter is one of those super annoying terriers that amps up any situation. And yours is compounded by 3 puppies. Maybe a puzzle feeder or something to make sure he is the last one finished.

Thank you guys! I noticed the problem started when the little one was out. She wouldn't leave Archer alone. Luckily she's gone back home now so I don't have to worry about that. She was a 3 pound puppy that loved to play with the big dogs and it got stressful. The only other time it happened is when Nikita wouldn't come in for dinner so I fed Archer in his kennel. When Nikita finally came in she walked right by him and sniffed and he flipped out. Harley doesn't bother him but that could be because Harley doesn't show any interest in Archer's food.

For the time being I'll make sure Nikita is already up before giving him his food. And look into slow feeders and see what works best! Thank you guys! I'm not sure if this should be classified as food aggression?? I can feed all three dogs treats right next to each other and he doesn't care. I guess I've just never seen anything similar to this.

We had a spaniel with major possession agression. If you got too close to his food or toy or him when he was asleep he would full blown attack. It didnt start until a stupid neighbor hit him in the head with an oak limb, but spaniels are known for doggy dementia and major behavior changes as they get older so i never knew if it was brain injury or genetic