Firslty, as you have stated sir that you father has passed away without any will.
Secodly, and also this is not the case where anyone’s name has been there as second holder in the flat.
Thirdly, yes, you all would have share in the property including your mom also.
Fourthly, you have to have that succession certificate to claim your right over the same.
Fifthly, for this you all need to apply before the civil court of law.
Sixthly, once you get that then your sisters may give NOC as for their respective shares.