Rehoming up to five stray cats

I've been taking care of a cat colony since April 2010. There are around eight regulars, including three kittens. The adults were at one time someone's pet. The three kittens were born to a stray cat (who has since disappeared) and I am the only contact they've had with humans. I can pet most of the cats when they are eating, and they don't run from me quite as quickly. One of the kittens likes to crawl on my coat--with me wearing it. Another kitten is probably too feral to be rehomed. Seven of the eight cats have been S/N and given shots; we weren't able to trap the eighth cat (male).
A friend of mine has converted a spare room in her house into a 'cattery', and has offered to take up to five cats from the colony to resocialize and adopt them out. She has lots of experience fostering feral and stray cats; indeed, that's how I was introduced to cats and Ritz in particular a year ago.
My question is: anything I should be aware of when resocializng / rehoming that many cats at once? I hope to trap together the cats who like each other (I can tell by their body language) and release the one or two who I don't believe can be resocialized. I am aware of and anticipate the 'vacuum' effect (one cat leaves, another one takes its place). And I know that rehoming feral cats is controversial; but based on the behavior of these cats, they are stray--formerly owned felines--cats.
Thanks for any advice.

Thanks LDG. Yes, this is the condo complex where a neighbor (now, more than one) is complaining about all the cats.
My FRIEND has had lots of experience, I've had practically none, and would like any “outside the box†tips, knowledge. I was wondering if there is anything different, unusual given that five cats, wide range of ages, will be trapped and relocated simultaneously. Will their social structure, interpersonal relationships, change? Is there anything I should look out for given that up to five cats – all from the same colony but all unique in their own way with different interpersonal relationships – will be resocialized at the same time? Could I expect different types of territorial disputes? Will the cats become jealous of one another if I give more attention to one cat than another? (This would make a great research paper!)
Good idea about the already socialized cats interacting with the newly socialized cats. The colony appears healthy; should they be tested for FIV/FELK before the two groups meet? The cats were given rabies and FVRCP vaccinations when they were S/N in early November 2010. Note that her cats are outdoor cats, and she has three dogs.
Thanks again.