1) I presume you are Hindu ---- I think you are victim some whare of confusion between HUF and non HUF and this lead to severe complication.
2) Land records where not checked properly nor updated. Only registered document under registration act is not sufficient you need to update land records to and that is imp.
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I prefer (Although document not seen, and may be not in language i can read so i feel with limitation i suggest and give random idea)
1) Claim adverse possession of Land which you have in possession That survey no. claim adverse possession. Against all people of that family every member should be made party to suit , additionally made new buyers also party , also make that whole buyer family party
2) Land which you have as per record or documents ---- Check the person who have possession and under which law and what documents he has. Local advocate can help . And put tresspass case against him, claim you are owner of that land and he is in illegal possession . Here also make all party , Previous owners HUF, you people, Person who is occupying that property his entire HUF
3) So you calim two land , 1)Which is in possession 2) Which you are there as per record
4) Regarding evidence creation local advocate can help you , because i don't know various proof which can be locally created. DO this with severe backing of evidence
5) Take Steps now within 3-4 months (See there is Limitation act after specific time dispute can not be taken that is after 3 years etc. Duration changes as per type of suit. So try to claim both land, other land you show he did encrochment now recently only)
6) When all lands are in legal dispute , give them option orally for settlement. In Court give application for alternate dispute resolution and tell we are ready to settle but we require land , this or that and as per money paid we require that area.
7) If nothing works out as per point 6 then try to best of your ability claiming both land. Second land due to limitation act may have problem but still try . Some time you too need to be crooked . Claim more land
8) Court fee you have to pay , that is expenditure apart from good land lawyers fee., But under Civil Procedure Code Sec.149 Court have power to allow you to pay fees at latter stage , or extreme hardship wave it , and if it feel the case is geniuene etc
9) Keep all optioin open for settlement.
10) Tell him to do rectification deed (Proper rectification to your original sale ded) . Do Cancellation Deed with new person whom he sold land. Correct all Land Records etc.
11) This all require good land related Advocate available locally . Jurdisction of Court wil be civil court which is close to suit land