Trinath From Secunderabad want legal help in Property / Ancestral Property / Will

We are two persons purchased a house. During registration of house third person name is registered along with me who not made any payments. Actually her sister paid all payments who is not in the sale deed. Now she, who not paid any amount is claiming the ownership. Is it legally permissable. If permissable what steps to be taken to avoid her ownership.
Secondly I occupied the house one year back and paying monthly rent. Total purchasing process like finding the house, talking terms to the seller and agreement was made by me. In the agreement the person name who not paid any amount to the seller and put in the sale deed is not there. Now I want to eliminate the binamy person from property deal. What to do. Please suggest.