Truthfully, I think you are asking for a great deal of trouble. Juvenile roosters tend to fight when they are flock mates that have been raised together as they come into maturity. A strange rooster will be considered as competition, which will make for very escalated fights.
And if by some strange unlikely event, they do get along, then your poor hens are going to be relentlessly over- mated and harassed. Juvenile roosters are very randy, and relentless. They tend to develop sexually long before the pullets will. They will get bigger faster than the pullets, this tends to make them into bullies. In my experience, roosters raised with just flock mates, often become very human aggressive.
Personally I would advise culling both roosters. However, if you have your heart set on having a rooster, keep the one you have, but keep a close eye on him for aggressive behavior. Be very careful with small children, as small children and women are who roosters tend to attack first.
Roosters can ruin the whole chicken hobby. Two roosters that are raised together with 20-25 hens might work if there is enough space. Adding a strange rooster to an established flock is very apt to be a major wreck. Cock fighting can be to the death. And if they don't kill each other the first time, they are generally willing to try it again.
It is a nice thing to do for your friend, but chicken society is very often not nice, and I really don't think this will work out.
MRs K
