Is the mother required to return the money she took from her children to build the second floor and prepare her sisters, knowing that she had previously paid off the father's debts and prepared one of her daughters?

Equipping the marital home is an obligation upon the husband, and the wife or her family are not religiously obligated to provide anything for it. Even if custom dictates otherwise, such a custom is corrupt and should not be considered, unless it is done by mutual agreement without compulsion.

Thus, the mother is not obligated to prepare her daughters' homes nor to buy the shabka (engagement gift) for her son.

As for the money the mother took to complete and furnish the house, there are two scenarios: 1. If she pledged to return it: It is a debt upon her that must be repaid when she is able. 2. If she did not commit to returning it: This is permissible if all the children are adult and mature. Otherwise, any money taken from a child who has not reached adulthood or maturity is guaranteed against her, unless it was spent for their benefit and with the guardian's consent.

Regarding the division of the inheritance: The mother receives one-eighth due to the existence of a inheriting descendant. The remainder is divided among the children, with the male receiving the share of two females. It is best to refer to the competent Sharia courts.