Im not an old timer or a professional chicken person. =) I have 29 chickens, have had chickens for about 4 years total, 2 of those years I have raised meat chickens also. This is my third batch of meat chickens, they arrived today.
First, I would say disease can be spread easily from wild birds, probably more easily than if you keep your meat chickens too close to your layers.
That being said, I think it is always possible to spread disease form one flock to another, in the same area. We have never had that problem here though, and ours have been close together, with my layers free ranging around my pastured chickens (in a tractor coop)
Then, you're not asking, but I would suggest getting more than 2 chickens for meat. Just because they may do better weight wise with more competition for food, and depending on the breed they die easily. We buy cornish rock crosses for meat.
(If you are just going to buy an all purpose breed and butcher, you may still want more than 2 for competition purposes so they get bigger in that time, though they are hardier)
But I am guessing since you said butcher in 6-8 weeks you will be buying a meat bird breed, in which case get more than 2 for the reasons I said above.
Hope that is a little helpful. Maybe someone else has different or better advise though =)
