1) muslim can bequeath only 1/3rd property by will
2)on your father demise your 3 sisters, brother and mothers are legal heirs .
3) flats cannot be transferred in your mother and brother name without consent of 3 sisters .
4) they will have to execute release deed /gift deed so that flats can be transferred in name of mother and brother .
5) on basis of release deed/ gift deed apply for transfer of flat in name of mother / brother in coopertaive society where flats are situated