Regarding the necessary parties

Sure. If the father is not in position to file a title claim his kids can do so. But this has to be such that the fathers name is on the new claimed title. Kids name can't come on it. They can fight cases on behalf of their father. Title will come to fathers name if original owner does not oppose.

Since property is in adverse possession and if you are the missing owner then you must go and take the land by force. Make sure you have that capability. Physical, finance, contacts, police, political backing are all needed. Such actions are not meant for most people. And do this only if it's a property worth crores. If it's only a few lakhs maybe below 10 - 20 lakhs then think twice if you want to take so much effort. Your time and energy may have much more value. Legal Adverse acts nullify illegal adverse acts. If it is a squatter case meaning that if the father in question was the tenant since many years and now he or children want it in his name then real owner can fight it out in court. Thousands of such cases in India. It will take 5-20 years to resolve. If you don't have strong finance or political power then be ready to fight this case for the rest of your life.