1. If it is your father's self acquired property (got the same from his father and subsequently registered Release Deed executed by his sisters in your father's favour), then it is your father's prerogative to give the property to anyone, including his children. Your signature is not a must for the self acquired property of your father during his life time.
2. Being the self acquired property of your father, he is well within his legal rights to give the property to only his sons.
3. Only in case of ancestral property, you would have got the right over the property. You will not have right over your father's self acquired property during his life time.
4. Your father's Sisters shall not have right if they have already executed registered Release Deed/Settlement Deed in favour of your father.
5. Your father's Sisters are free to challenge the Release Deed or Settlement Deed, as the case may be.