1) your father has merely named you as beneficiary in the will
2) to apply for probate notice has to be issued to all legal heirs namely brother mother two sisters
3) after receipt of notice your sister can oppose grant of probate . if the they do so then it would be converted into testamentary suit and you will have to prove the will with help of the witnesses
4) your sister can cross examine witness
5) court will pronounce order after considering evidence led by both parties