I have three of these that need merging and can I do this and not have someone unmerge them.
Given that "unmerge" becomes unavailable as soon as any other edits are made to the profile (including merges of family members), it's pretty highly unlikely to happen.
But why are you worried about someone undoing your actions? Is the equivalence of the profiles uncertain or controversial? Since undoing an incorrect merge is complicated, it's best not to do them if there's any doubt. Do more research first.