I absolutely agree that they will not sell all three properties in time to relaunch this show in their stated time frame. Depending on how much they have in the bank, they may not need to. As far as the warehouse thing, It's possible. The only difficulty is running enough power to operate a whole fake house. They could rent a couple big generators. Sound stages for professional films are built with that kind of power draw in mind, regular warehouses are not. Professional sound stages are very expensive to rent for the 3 or 4 months they'd need one for, and buying one would be even worse. Building one may not be too bad but idk what the zoning requirements would be and it would take years.
They'd have to put more effort into this than anything they've done so far, so your concern is valid. Hard to say if they'll manage to pull something out of their ass and make it work before January.