What is the share of each heir from the estate of a deceased father who left four children (two sons and two daughters)? And is it permissible for the eldest brother to disinherit the two sisters?

It is not permissible to deprive daughters of inheritance; this is one of the major sins and is considered consuming wealth unlawfully. The verses of the Holy Quran explicitly state that women have a prescribed share in inheritance, and that the male shall have the share of two females. This is agreed upon by Muslim scholars. Whoever does this has violated the Sharia and the sayings of scholars, and has imitated the practices of the pre-Islamic era of ignorance (Jahiliyyah).