1. Well this is pretty much common ailment afflicting most of the joint households.
2. It is true that your father can not unilaterally sell the ancestral properties though he is very much within rights to do so as far his self owned properties are concerned.
3. Since here you are concerned about the ancestral properties then immediately file a suit for partition wherein you can claim your dues share the list of ancestral properties.
4. The to ensure that the said properties may not be sold during the pendency of the suit to frustrate your claim, you seek injunction in the same suit as well so the court puts a restraint order in place so no property may get sold as long as the suit is not decisively finished.