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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
A person who is capable for disposing his property may dispose of all his property by gifting it, giving it in charity and the like, to render the one to whom it is given as the real owner of the property to who may dispose of it as a real owner does. However, if the gift is conditioned on the death of the donator, then in this case, it has the same ruling as a will. A will is not permissible for a heir and it should not exceed one third (of the inheritance) unless the other heirs who are adult and some approve it. Nonetheless, it is not permissible to do any of the above with the purpose of preventing the heirs from their rights which is determined by Allaah in His Book and on the tongue of His Prophet and whoever does so, is treated contrarily to his purpose.
A father is obliged to be just when gifting his children. If he gifts some of his children without gifting others or he favours some of them over others when gifting them without a valid reason, then he is sinful and he is obliged to repent and do one of the two following matters:
With regard to your situation, it should be looked at whether or not there was a sound reason for your father in favouring one of the children over others, and the gift was at the time when he was in sound health, then the gift is valid for whoever has taken possession of it. The gift of the father to the mother should be looked at in the same manner; if this happened when the father was in sound health and the mother had taken possession of it, then it is valid. Otherwise the gifts should be put back in the inheritance and them it should be divided between the heirs in an Islamic and legitimate manner.
It should be noted that it is only the judge that can solve the disputes, or an Islamic judgement if there are no Islamic courts in your country. Finally, we advise you to be kind and dutiful to your mother and to keep ties of kinship with your brothers and sisters. You should also try to be kind and affectionate with them, solve the matter in a friendly manner and in a religious way that allows keeping ties of kinship between you.
Allaah Knows best.