Just because your cat is little doesn't mean she can only have a couple of kittens.
There are 95,000 cats looking for homes on Petfinder. Wouldn't your little brother be happy with one of them? I bet your local shelter has a dozen kittens that will be euthanized if they don't find homes. Couldn't your brother be happy with one of them?
I don't know about your vet, but every vet I have ever met is much more impressed by people who DON'T breed then people who do.
Please, do a little more research on the complications that can happen in small pregnant cats. We can't diagnose your cat over the internet, so you will have to wait and see what your vet has to say.