Is you place fenced? it will make it easier to get them back in they herd really well.
Okay well you may have some problems maybe not just take it as it comes. My Muscovy drake loves to fight when he has the upper hand it's funny because Sam my gander is the head one during late winter thru...
Let them live side by side till weekend then do you ever let your flock forage out of their pen? If you do then come the weekend try letting them all out on neutral ground there maybe some pushing and shoving but hopefully that will be all. What age are your Muscovy and are there drakes? asking...