Hello Steward,

If the contract is real; that is, that your mother signed it and agreed to that deal, it is certainly valid. However, in order to complete the transaction, the buyer must obtain the heirs´ signature. The heirs can oppose if they consider the sale was agreed under duress, taking advantage of state of necessity or dementia from your mother, as the agreed price is well below the market price. If the heirs can prove that before the judge in a court claim, the contract would be rendered void. If they fail to prove it, they must sale the property to the buyer at the price your mother agreed. If the contract does not bear your mother´s signature, the buyer will find it more difficult to prove he had a solid agreement with your mother.

Regards,