I bought a piece of land in the outskirts of Enugu town in March this year. The original allotee of this land is dead and so the seller of this land is his son. The son claims that the father transfered this land to him via a deed of assignment thumbprinted by the now deceased man. A second man bought this land for 400k and sold to me. I paid 600k to the second owner and moved into the property where I brought in about 12 trips of sand and made 2900 pcs of blocks, 80 bags of cement.

Trouble started immediately I dug the foundation of my house, the next day youths invaded the plot, claiming ownership of the land. According to their leader, the land belongs to his father and they are not aware their younger brother sold this land. They covered the foundation I dug and threatened to destroy my blocks if I go any further.

I have the only original allotment papers to this land and other documents like
The tranfer document with which the son claimed his father used to give him the land.
The deed with which the second buyer bought from the son.
The deed which I used to buy the plot.

The first son of the man arrived today and gave me a call to have a meeting with the family this evening, and I need to know my rights in this transaction.
Can the transaction be revoked under the law because it was not the first son that sold the land.
Can they legally claim for the land even while I have all the right papers.
Supposing the first son declares the document stolen, can I be arrested.
If the first son obtains a letter of administration, can he claim this land from me.
I have a feeling they may want me to come up with more money since they need cash now, their mum just died.

Please, all the gurus in the house, advice me before I step out for this meeting, so I can know how to play. Either to call their bluff and fight my way through or sue for peace and seek for settlement.

Thanks in advance.