Registration or Regularising

Hello to all, The flow my issue is as follows- 1. My dad has received a property on the basis of a GPA (unregistered) in the year 1990. It was not registered as the Govt. had stopped registration at that point of time (may be for few years). There is an express clause in the GPA, stating that owner himself will come and complete the registration in the future after govt. resumes registration. 2. Years flew by and my dad was least bothered of registration as he did not have any knowledge on the same. Also, he never understood the documentation regarding land. 3. Somewhere in 2004 or 2005, daughter-in-law (representing her husband) of the property owner showed up, out of the blue stating that property belonged to her and we have encroached using some illegal documents. Ours was not the only property in jeopardy but the whole layout was, as the seller was the same for all and the status of all was the same as ours. 4. She appears every now and then and stops, if any construction work is undertaken in any of the land located nearby. 5. We are paying the applicable property tax for more than 8 years now. Also, electricity bill is being generated in dad's name since 1992 as we are in occupancy from then. Queries: 1. Is she correct in her stand? 2. What is the remedy left to us now? We have to regularise the same now, very soon. 3. What is the applicability of akrama-sakrama on the above? 4. Can it be registered in son's / daughter's name, now so that it will be regularised? Kindly, do the needful as I am desperate to sort it now. Looking forward for your expertise on the above.