Re-introducing kittens

I'm new to posting but have read several of the posts, so first off, hi Okay my questions is does anyone have experience in re-introducing littermates to each other and how difficult is it?
My boyfriend and I took in four littermates this June, he took a pair and I took a pair. I was planning on getting two and when he heard that the remaining two were going to be taken to the pound, he decided to take them until he could find good homes. Well naturally, they're not going anywhere as he loves them to death. They are currently living at his house with his roommate's three cats. They all get along and there haven't been too many territorial issues. My two kittens live with my cat Sasha and other than the occasionally kitten smackdown by Sasha, they all get along.
My boyfriend's roommate is moving out this fall and I will be moving in when my lease is up. We're just wondering when we do combine them how difficult it will be to re-introduce them. Do we do it as if they've never met before? Just for age references when we move in the kittens will be 7 months and Sasha will be 2 1/2yrs. The kittens were about 2-3 months old when we got them. Will they remember each other after 4-5 months apart? TIA!

As long as everyone involved is neutered/spayed, things will go a lot better. They MAY remember each other, but is more of a chance they will act like "strangers". So go with as if they were not related at all.

I'd try some of these things when introducing face to face:

1. Sprinkle cornstarch baby powder on everyone so they smell the same.

2. Put a dab of vanilla extract on each of other noses.

3. Give everyone a bath in the same kind of shampoo so they smell the same.

It is great that you are being extra cautious with this situation. Your concerns are definitely valid, this is a sensitive age for teen kittens to meet others even if they are siblings. First thing is for all to be neutered and spayed of course. It is best to introduce them as first time, especially in Sasha's behalf. The intro of new kitties to home should be their own room, litter, food, water. Allow all to smell each other under door and allowing the newbies to this home to feel comfortable and secure in a room of security. I would also suggest trying to reintroduce the kittens first, maybe carry one out at a time with the others, see how it goes. It may take a few days, even longer, or less. It is best to protect any immediate conflict and take it slow, so much easier then trying to fix a problem then to avoid one all together!