Family Dispute

We are having a shared corporation water connection which we are using for 20 years. Separation of business happened five years back. This water supply line is not in our name. The other party has asked us to get a separate connection and bear the entire cost. We asked them to keep it as it is as they are not going to contribute to get that done and they are now threatening to make a police complaint if we stop them from making modifications to stop our water supply. The second thing there are many other internal matters where we were supposed to get our money from them but they are not willing to give it. We don't have a proof for all matters but can try to get proof for certain things. We simply asked them to at least return our money back so that we can utilise it to get a new connection. Please advice