Is it permissible to carry out the deceased's will to allocate 50,0 [currency units] to each of the three unmarried children to cover their marriage expenses before dividing the inheritance, and to postpone the division of the house until the mother's death, with the mother remaining in it?

The father's will not to divide the house before the mother's death is not legally binding. The house becomes the property of the heirs immediately upon his death, and each of them has the right to claim their share. Likewise, his will to give a portion of money to some children in exchange for marrying off others is invalid and not enforceable. He is not permitted to bequeath a reduced share of inheritance to one of his children in exchange for marrying them off.

If the deceased left behind his mother, a son, and seven daughters, the mother receives one-sixth due to the presence of a lineal descendant. The remainder is for the son and daughters by ta'sib (agnatic inheritance), with the male receiving the share of two females. The inheritance is divided into 54 shares: 9 for the mother, 10 for the son, and 5 for each daughter.

If the "mother" mentioned in the question is the wife, she receives one-eighth due to the presence of a lineal descendant. The remainder is divided between the son and daughters, with the male receiving the share of two females.

It is important to note that matters of inheritance are precise and complex and cannot be resolved merely by a fatwa. Instead, they must be referred to the شرعي courts for investigation and verification to ensure there are no other heirs, wills, debts, or rights that take precedence over the heirs' rights.