
I have Muscovy and can honestly say your drakes are going to fight when hormones hit. Most drakes will fight but Muscovy are fierce fighters. If one doesn't have a way to stay away from another there could even be death. Or the one being singled out will fly away.
Your Indian Runners will probably be in trouble too if any of the larger drakes go after them. My Muscovy drake pays no mind to my Runner drake of his females but he has his own females so he's a happy boy but I could never have another Muscovy drake [I've had as many as 4 and to keep the peace each drake had to have his own space with his own girls] Others may have a different situation but this is how it's been here.
@Canadian Wind has multiple Muscovy drakes maybe he can weigh in. Not sure if any of his are of breeding age.
I haven't ever had Cayuga so can't say much about them but from being on here for many years I can say most drakes once hormones kick in are going to fight just some more than others. Plus unless the females are separated they are going to be abused and injured. Drownings in pools is one way and that has happened just recently with one member. Drakes will gang up on females in water.
If your parents don't want to part with any of these drakes then there needs to be a plan to keep the females safe and the drakes safe from each other too.