Any need to quarantine?

I have friends who due to health reasons are no longer able to care for their 24 12 week old chickens so I have agreed to take 5 or 6 off their hands so they will have a life as layers instead of becoming dinner. These birds are the same age and from the same hatchery as some of mine but have been living in a coop where a previous owner kept approximately 100 meat birds.

I've read that it is not advisable to keep young birds in a coop that was used by another flock, and as this is the situation my friends birds have been living in, should they be quarantined before being introduced to my flock? If so, what should I be looking for to determine they are not carrying a disease they may have picked up from the coop they were living in? I've seen my friends' chickens and they look perfectly healthy, but then I'm new to all this. If my friends birds were in a coop that had not recently been used by other chickens I would probably not worry about this at all.

I am currently in the process of introducing 26 12 week old chickens to 2 six month old hens and a six month old rooster (I had half the coop divided with chicken wire with the younger birds on one side and the older birds on the other (with access to outside). On Sunday I opened part of the divider and the younger birds have been venturing into the other side. The older birds peck at them but it seems to be under control). I will not be getting these additional chickens for at least 4 weeks, by which time I suspect our young and old chickens will be completely integrated with a new pecking order. What is the best way to introduce the 5 or 6 to a flock of 29?

Thanks!