I am sorry to hear about the loss of your hens and roo:(
If I read your post right you are getting adult hens and roos? Make sure you are getting them from someone you know and trust-You still need to watch for signs of mites, worms etc...I would probably isolate them and treat thems for mites etc.... and then introduce them to your flock - Do not just let them fend for themselves - put them in your coop but in their own cage,pen - this way everybody gets to see everybody else but they can't peck at the new girls, everybody does a little meet and greet everyday. I would do this for about a week or two and then when I did let them out I would watch them and make sure no serious fights broke out, and maybe only leave them all together for just a couple hours at a time. This is just my opinion, just be patient with your girls. And again be careful who you get your new girls from, you can wipe out your whole flock.

We will want to see pictures of the new girls/boys:)