Not sure how well the "Ownership and control" page explains it, but basically, once I've added my own research or family information to wikitree, it is no longer "mine." I've contributed my information to what will ultimately be a single family tree. And by doing so, I agree to collaborate with others.
The best way I have to correct mistakes-- whether by myself or others-- is by finding and citing quality source information that makes it really clear what is accurate. In the absence of quality source information, we have to assess what evidence IS available and make the best case.
In the merges you describe here, this is an opportunity to partner with the other profile manager to find the best, most accurate information. And... connect with a possible cousin.
Let us know how we can help you.