Co-ownership occupancy rights

We are one of the co-owners of the property that belongs to 4 families. One of the families is living in that property. They are neither allowing us to sell it nor letting us to occupy our share. Even we want to live in that house but every time we bring up the topic, they start fighting with us and ask us to leave. Because they have been living in that house, they have been paying the tax, electricity bil However, the registration is still in the name of the co-owners mother (who is no more). But as per the Ghaziabad Development Authority, the house belongs to all the four co-owners, equally. They also say that they have spent money on developing the property further - but they have not constructed it as per the Ghaziabad Development Authority's approved blueprint - which means it is an illegal construction. Can we also legally start living in that house, like that family does? Do we need to give them any legal notice, before entering the house - is it a court case or just a safe entry? Will the local police be able to help us in this matter and how? In case we all arrive at consensus to sell it, can they claim the cost of construction - which is illegal? Can we ask for compensation for the stress we have gone through all these years and for using our share for free - we have been living on rent because of them? In case we want to execute a partition deed, can anyone challenge its proceedings - because I feel an ancestral property anyway belongs to all its heirs?