Ownership of property

We are staying in our house for 20 years, which is unregistered. This house was in possession of Christian missionaries at the British times. While leaving they gave the house as enjoyment land to our previous owner (now dead). This cannot be registered as there is some confusion at higher level of current missionarie management. So when we bought house from owner(children), we took signatures from all children in the aggreement by paying the agreed amount and staying there for more than 20 years. Now they are creating havoc and trying to take possession of the property. The only thing they have on their side is property tax Name, which is titled to their father. We have an agreement, and electricity bill (on our name), gas bills and Bank statement and aadhar etc.. Is there a way to change the title of owner in property tax with the house being registered? What are the odds of other party trying to get the property? If we pay tax for the property which is not our name will it favour the other party? We are staying in the house for more than 20 years with out any interruption. So will that make us the owners? Please help considering all the facts above Thanks