What is the ruling of Islamic law on changing the wording of a contract for the sale of a shop – an inheritance – such that the second party in the contract becomes the daughters of the questioner's paternal aunt instead of her deceased husband, in order to deprive the deceased's mother of her inheritance?

It is not permissible to change the صيغة of the contract so that the buyer is someone other than the deceased paternal uncle, due to the potential deprivation of his mother that could result from it. If the paternal uncle purchased from their money, then this must be proven with evidence, not merely by a claim. It is enough for you to please your Lord, even if people become displeased. We advise you to counsel them and explain the truth to them gently and wisely.