Having reread the OP, I think the solution, without causing a family row and too much trauma, is for one of you always to be there so that the GS always has to sleep on the airbed. I assume, when you are not there, he sleeps in the bed. You could also throw redecorating the place into the mix. Failing that, rent flat out to him at the market rate and stay in a hotel for the odd night you are in London.
Reducing contact because my heart just isn't in it.


