Day 1 of nonsense: Why is this allowed?

[not_ya_wify]

Housing has multiple uses, and SE has decided intended or not that they will allow players to have multiple FCs with houses per world.

They don't. If you are in an FC with a house (even if you don't own the FC), you cannot bid on another FC house with an alt on that same account. Not even for relocation. I have my own FC on my main but made an alt that was in another FC trying to relocate to a larger plot. I tried to help them bid on the larger plot and the game gave me an error message that I'm not allowed to bid on anymore FC houses because another character on my account already has an FC house. Which is pretty stupid since that FC already had a house at the time and was merely seeking to relocate, not buy a brand new house.

[Reinha]

If you are in an FC with a house (even if you don't own the FC), you cannot bid on another FC house with an alt on that same account. Not even for relocation.

You can, sometimes. You can bid on the alt and the main if neither your alt or main bought the house for their respective fcs.

Here's the simple version:
-Did you buy any fc houses on this server? If no, all characters on your account can bid.
-If yes, is any buyer character still in the same fc they bought the house for? If no, all characters on your account can bid.
-If yes, that buyer character can relocate the fc house they originally bought but no other characters on the account can bid.

The game functions exactly how the rules are written:

You do not have a character on the same World on the same service account that purchased and maintains a free company plot
* If the character in question purchased the plot, they may still submit a lottery entry for the purposes of relocation.

"Purchase" means you spent the money and bought the plot. "Maintain" means you are still using it, in other words you are still in the same fc and the plot has not been demolished. If you didn't "purchase", the restriction doesn't apply. If you no longer "maintain", it also no longer applies in that case.

[Jojoya]

They don't. If you are in an FC with a house (even if you don't own the FC), you cannot bid on another FC house with an alt on that same account. Not even for relocation. I have my own FC on my main but made an alt that was in another FC trying to relocate to a larger plot. I tried to help them bid on the larger plot and the game gave me an error message that I'm not allowed to bid on anymore FC houses because another character on my account already has an FC house. Which is pretty stupid since that FC already had a house at the time and was merely seeking to relocate, not buy a brand new house.

You can bid on additional FC houses as long as any alt on the acount that previously purchased (or paid to relocate) a house for a different FC is no longer in that FC. That holds true even if you have other alts still in that FC. They did not purchase the house so their presence in the FC, including as FC Master, has no impact.

Not going to say I like it but that's the way that SE has built the system. Only the character that actually made the purchase of a FC house already acquired matters when it comes to whether or not you can purchase additional houses. Remove that character from the FC they purchased the house for and more house purchases are fair game for any character on the same world/service account. That's been tested pretty thoroughly at this point.

That's why I'd rather see a system where "ownership" is tied to the FC Master and not the purchasing character. Despite fears that it would prevent transfer of FC Master in case of absence, it's going to be a very rare FC that doesn't have more than one eligible member.