Housing is instance and does cost gil. What you really want to is to limit housing to one per account and removal of plots, apartment, wards.

Also only one FC can own a house. What you are seeing is a FC that is really broken up into multiple FC that use the same FC tag owning multiple houses. The FC is called FinalFantasy123 (FF123) but one house is owned by FC: FinalFantasy123workshop (FF123), FC: FinalFantasy123gym (FF123), FC: FinalFantasy123lounge (FF123), etc...