Is it permissible for the heirs to take money from the new owner in exchange for waiving their right to the shop that devolved to them from their father, and what should one of the heirs do with his share if it is not permissible?

The questioner did not specify the nature of the old contract. The perpetual old lease is Islamically invalid. It is not permissible for the tenant or their heirs to prevent the owner of the shop [from reclaiming it] or to take a sum of money in exchange for vacating. It is obligatory to return the money if they have taken it.