All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
The wealth that your father left after his death is a right for his heirs. You have to give them this money immediately and it is not permissible for you to delay dividing it among them without their consent. It is better to divide it immediately to avoid disputes and problems. Your mother being of an old age is not a religious obstacle in dividing the inheritance and specifying her share. If you fear that there will be disputes regarding the division of inheritance, then you can take the matter to an Islamic centre to deal with it.
If the situation is as you have mentioned that your father left a wife, a son and three daughters, and that he had left 30,000, then this amount should be divided as follows:
The wife will get one eighth from this amount which is 3,750.
The male will get a portion equal to that of two females of the remaining share. So the share of the son is 10,500. Each of the girls will get a share of 5,250.
As regards the second issue, if you mean your mother, then it is not permissible to divide her inheritance while she is still alive. However, if it is a separate question that has nothing to do with you, and the mother left the heirs that you mentioned, then they will inherit her as follows:
The male will get a portion equal to that of two females. So the share of the son is 37,000 and the share of each girl is 18, 000.
Allaah knows best.