Black Australorps, Buff Orpingtons, Wyandottes, Jersey Giants, Barred Rocks....all great breeds. Friendly, docile and great on the laying.
When you want to mix new birds into an existing flock, it is best to keep the new birds in a cage or fenced off area but within the flock at all times...
Hello there and welcome to BYC!
Oh, I am so sorry about all your birds! Definitely post this in our emergency section for more help. I hope you can figure out what is going on.