Is it permissible to pay for the tuition fees of younger sisters from Zakat al-Mal, given that the father does not provide for them and the son works abroad and sends them money?

It is permissible to cover the educational expenses of sisters from zakat if they are poor and unable to combine studying with earning a living, and if their father is unable or unwilling to spend on them. This applies whether the knowledge is religious or worldly, as long as it falls under the category of communal obligations (furood al-kifayat).