Is the father, if he is mentally ill and in prison, entitled to custody of the daughters, given that he refuses divorce? And to whom does custody transfer after the mother? And is the paternal grandmother entitled to custody?

A wife being harmed by her husband's illness permits her to seek divorce.

Custody belongs to both parents as long as the marriage subsists. If they separate, then custody belongs to the mother, by scholarly consensus. After the mother, custody transfers to the maternal grandmother according to the majority of scholars.

Child support is obligatory upon the father.