It's an interesting problem, one that needs organization to manage all the data, and filter out the irrelevant.
My main suggestion is to "fish in every pool", applying that 2 ways. First, you've got a good start by trying ancestry, FTDNA, and GEDmatch, but you may also want to upload to MyHeritage too, and possibly Geni.com also (although I find their DNA support to be very weak, over-hyped). What you want is to find that tester who's a closer relation, whose ancestry trail will cross yours at a more recent ancestor. That would help you eliminate a number of descendant lines from previous generations.
Second, looking in more databases may help you find more of the right descendants. You're looking here and on Ancestry, try also FamilySearch and Geni.com. Both of them are huge and are free or allow free usage, enough to investigate families and descendants. As you probably know, no database is perfect, and all of them (including WikiTree) have numerous profiles with no sourcing or evidence and unreliable information, but all of them do have valuable data that's different from anyone else's.
A last suggestion, to help organize it, determine which ancestors look the most likely and consider them anchor persons, and concentrate only on descendant lines that include them, checking every database for what they have on them and their descendants. At any point, you can drop them if nothing is working, and appoint a different person as your anchor, on probation if you like. You probably have your own methods, but I get overwhelmed at times, when there are too many choices or ways to go, and I need to find a focus to concentrate on, knowing I can change it later.