Hi John.
Yes reverse dominance does occur especially when young swans start their own families. These fights may go back and forth but unless there is a chance that adult swans or cygnets are going to get severely injured or killed they will need to work it out. The only other solutions are to find another home for the younger pair or keep them in a pen with their cygnet for a couple of weeks until the older pair reassert themselves or both males' hormone levels settle.
The Regal Swan