Now, granted this is going to piss people off, but whatever. People have inactivated subs due to poor housing system b/c they can't get one for whatever reason. Situations like this in the photo should never be allowed to happen. It's unfair to anyone trying for a house, and it's a loophole SE should have thought of LONG AGO. Multiple FCs do this, as well as players with several alts.
You are allowed ONE FC HOUSE, if your FC already has a house, you cannot purchase another. That's the rule, the loophole is simple. Make an alt, give it a FC by itself, rename the tag to your original FC. Once that's done several times, it looks like this - or, another member makes a random FC and renames it's tag, whatever. It's still a plot being used to benefit a specific player/FC. If you have the ONE FC HOUSE rule, but implement ACCOUNT-SERVER-SHARED HOUSING, it's impossible to loophole. All 8 characters on a world server would share a single plot, which would be cool because you'd always have a house, even on an alt without having to spend gil more than once.
Solution? The people doing this do not care about other people having the same opportunities they have with housing since they own multiple plots. "Well, I have the money, I was here first, etc" excuses should only be valid on that first come, first serve basis for buying a plot of land. After that, congrats you have something, now stop being greedy and let the rest of us get a piece too. Take the biggest plot someone owns on an account/world and make that their house plot. refund their gil from other plot purchases and return their items from other plots to the resident caretaker. 1 person may quit b/c they don't like this, but you just gave 7 other paying subscribers an opportunity 1 greedy person prevented them.
Two FCs cannot share the same name, so why can they share the same tag? Correct this, and we will stop seeing the situation where it appears the same FC has multiple plots. You also have people owning an FC when there's only 1 person in it. To remain as an FC, it should have 3 DIFFERENT PLAYER ACCOUNTS with members. You need 3 signatures to make an FC, so there should be the same requirement to keep 3 different members (not your main and 2 alts). This would also prevent people from making an FC just to buy an additional plot of land because, again, account housing...
Implement instanced housing. Apartments are a good example of how these work. Why can't you use the same system, but allow someone to choose the size of their house? It can be like a condo building. Condos appear similar to apartment buildings, but different sizes...