What do the rest of the family want to do?
I've seen some cases where half the family want to realise their value and the other half don't want any aggravation, even if that means the "stay in the house" staying permanently in the house.
Is it possible that his share of the sale of the house, if it happened, would enable him to buy elsewhere? Even if that was with help from other members of the family?
Are the family willing to seek a Court Order evicting him from the house? And going as far as having the Sheriff forcibly removing him?
If not, and if the sale cannot be achieved by peaceful means, then it is a matter of waiting it out. Eventually, many years into the future, the house will probably become derelict and Lord alone knows what will become of the incumbent.
mf