He does not want to sell and is attempting to get the rest of the group to allow him to buy them out at a price he cannot refuse, ie a lot less than the agreed value.
Therein I suspect lies the real issue. The "agreed" value is almost certainly not what it would fetch on the open market.
Why not suggest it is marketed and then he, with his intimate knowledge of the beast, can bid a quid more than the best offer and buy it if he wishes. That way is fair to all (except perhaps the poor sod who puts the offer in).
It's not unreasonable to expect him to pay a fair market price and for the others to accept market value rather than a figure they would like it to be worth.
Mike