Is the document written by the sister to her brother (such as a sales contract) considered a waiver of the house as a will after her death, and do the siblings have the right to claim inheritance in the house, and what is the legal heir's share of the inheritance?

If the house is owned by your sister's husband, your sister inherits only one-fourth of it if her husband has no lineal descendants, and the remainder goes to the husband's uterine relatives.

If your sister has written a document relinquishing the house to you, this relinquishment is to be considered:

If she intended for you to take the house after her death, it is considered a will and cannot be enforced without the consent of the heirs if you are an heir. However, if she intended to gift you the house during her lifetime, it should be considered whether she gifted it to you while she was not suffering from a life-threatening illness and whether you took possession of it during her lifetime.

To determine the share of inheritance, the heirs must be identified. It is preferable to refer the matter to the Sharia courts or consult scholars directly to confirm the heirs, debts, and bequests.