they shipped me Barred rocks and EE's. From what I see, the BR get to about 7-8 lbs and the EE stay about 4-5. Is this going to be a problem?
I don't know where you get that EE's are only 4-5 pounds. EE's are chickens that should have the blue egg gene. They could be tiny like Seramas or huge like Jersey Giants. You may have some specific knowledge of where they came from so you have a good handle on their potential size, buy if this is from something general, it is not necessarily so. Other than the blue egg gene, there is nothing general about EE's, size, color, pattern, anything.
Most roosters are bigger than the hens of the same breed. When they mate, the hen flattens herself on the ground to spread the rooster's weight into the ground. While the more difference there is in the rooster and hen size the more chance of a problem, many people keep bantam hens in the same flocka s regular sized roosters and don't have problems. They are living animals and anything can happen, but I personally would not be worrried about the size difference you mentioned.
I had also planned on letting my original order interbreed since the breeds were closely related anyway. But now that they are so different, I may breed them seperately but I don't have the room for two coops. Can I keep one roo of each without having a bloodbath?
Probably. Sometimes roosters will fight to the death. Sometimes. Usually, especially when they are raised together but even if they are not, they will reach an accommodation and work as a good partnership in protecting the flock. Some of the time, what fighting there is consists mainly of chasing and running away. Siometimes they will square off and go at each other, and sometimes one gets hurt, but usually this quickly becomes running and chasing.
They will not only mate with their own breed. They will both mate with all the hens regardless of breed. Studies have shown that the non-dominant rooster fertilizes his share of the eggs.
I also received a Salmon Favorelle as a mystery chick. They are only 7 weeks old and she already seems like a loner(she is the smallest). Is she going to be okay?
I expect she will. Many people raise bantams with full sized fowl and they do fine together. With chickens, size is not as important as the spirit of the chicken. In some flocks, the bantam rooster dominates the full sized one.
