Neighbour occupied toilet in common area

Dear Sir, In our building we are 6 flat owners in Ghaziabad. One of the family is always shouting and misbehaving on trivial issues with all of us and other people in the vicinity. Recently, our watchman has to leave job because of their misbehavior. Now that the watchman had left, they put up a lock on the toilet which was used by the watchman earlier. All of us are feeling that how could they lock common area illegally and without our consent. No new watchman is ready to take up the job in our building for non-availability of the toilet. This toilet comes in the common area of the building (in front of their door at ground floor) and not owned by anyone of us. They say the new watchman can use public places as toilet for him and his family. House lady and her daughter have threatened that if anyone will try to break open the lock of the toilet, they would file a police complaint stating our names as trying to molest. Her husband is loud and ready for scuffle. Payment of their monthly dues is also pending for few months and they also do not generally contribute in major expenses required from time to time. We are very peace loving people and no one of us dare to face them to avoid any unwanted consequences. We are bearing them for many years and as a result of which these days their menace is peaking. Please guide what can be the legal recourse available in such a case. Thanks in advance. Your truly, Rajendra Prasad