I'd say it is kind of normal. I fyou had more female mollys he may lose interest. Seperating him likely will not help. Here is the problem I see, mollys get large and I doubt it would be wise to add more. You may wish to remove him for a day and see it the other male molly picks up where he left off. Is he trying to mate the platys? That would be typical as well. If you remove him and things settle down then rehome him or return him. These animals may not be rocket science material but they all have a personality.