Re: HELP PLEASE! Two kittens - aggressive behavior
I have never had to do the proper introductions either BUT, some cats really need it done, so it's always best to start out that way to avoid possible problems. That being said, i understand you have a space issue but, don't you have a bathroom where one kitten can go for a little while? Let them both settle down and start over.
Crating kittens, is not the best idea unless it's for very short periods of time. Kittens have way too much energy and curiosity and need to race around like crazy and explore. Being in a crate can cause them stress and frustration which could lead to aggression. They have way too much energy to burn and, if you have them crated and then put them together, it's not surprising one or both would go a little nuts.
I would clear out the basement asap and move them where they have some space to run around. In the meantime, at this point, it sounds like you really have to find a way to separate them for awhile. Give them a week or two to chill. Play with them TONS to expend as much energy as possible. While they are separated, swap smells by switching bedding and towels and such so they get used to eachother's smell. In a couple of weeks, try introducing them again. First just let them see each other. Before you put them together, get them all tired out and feed them a good meal.
Google cat introductions and you'll get more suggestions.
I know it's probably not exactly what you wanted to hear but I hope it helps.
I doubt your 11 week old is actually being aggressive. It sounds like he's just a bundle of energy and doesn't know any manners yet. They need to be taught what's okay and what's not. When you say he was aggressive with you, what exactly was he doing?
Also, at 7 and 11 weeks, they should actually still be with their Mums. Way too young so they will need some special attention and care for a few weeks. When kittens are able to stay with their Mother and litter, they tend to be better "behaved" cause Mum and siblings teach them some manners. You're going to have to do that yourself now. But that's a whole 'nother post!