Oh, one other thing-- the nipping and snapping is normal. That is Molly's way of telling him to back off. When that is happening, let them do their thing, they will work it out.
When they are truly fighting-- which can come about quickly- and they are using teeth/breaking skin, you have to step in calmly and pull them from behind. Grasp onto the collar and pull up and back gently.
Every instinct is to put yourself between the two of them and shriek but that isn't helpful and is dangerous.
(PS: Ask me how I know
)
I know that is the worst thing to do and if I could take a guess, we did it wrong 99% of the time.
Hopefully, you won't ever need to deal with this scenario but better to be prepared than not.