At this poin in time, there is no system in place to transition a pre-constructed/owned house from FC>personal or personal>FC - while some people are wanting to see this ability put into the game, there are many other facets of the housing system that need to be improved on before they can focus elsewhere. So for the time being, your options are either a) hold off on buying a place when the new wards are out (who knows when that will happen) and stay in your current FC or b) set up a linkshell with everyone in your FC so you can still communicate with everyone en masse, leave & buy the FC attached to the house you mentioned in your post.

It might not be an ideal set of options, but that's all there is at the moment.