conditions in the settlement deed

It is the mother who may dispose it in terms of settlement.

However, father has no right, interest, claim or title over the property acquired by mother.

In this case father is not alive. mother has life interests to live in the house and enjoy profits in the said property. but now son wants to sell the entire property with the consent of mother.but in the settlement deed father made a condition that this property can't alienated till the death of himself and his wife ie. here is the mother. so his wife can give a consent to sell the property by avoiding the conditions in the settlement deed