Civil case: we have patta on land but opposite party is fighitng?

We bought half of the house (700 sft)5 years back (approx) on dec 2005 from a guy. last may he sold out remainig half the house to his relative.Now his relative is fighting with us to give that land.But land seller is supporting us and he told to eveyone, for my hungry only i sold the land to him. actually he is a bachelor, and he is 40 years old. This land was in the name of his father now it has been transferred to him and we bought that one.and also we got patta for that. Now seller father sibling son is fighting with us.he is saying ” give that land or else i will register a case in court like he mentioned, we did not get our proper wealth.”what can we do now? will the land belong to us or the seller sibling sons. As of now seller father was died 10 years back. 2) when we register the land , that time we mentioned in stamp paper , this is empty plot and there was no house on that. actually it was a damaged house , so we mentioned like that,. will it create any problem for us. but opposite party mentined house in their stamp paper. let me know your answers.