Upvote:3
A simple statement should be enough, essentially an invitation letter, saying your parents will visit you in your home (note the address), a private property, during a specified time period (note the dates), and that there is enough room.
While it is unlikely that proof of ownership is requested, Council tax addressed to you at the new address should work. If more is needed, an executed sales contract should suffice, as the property conveyance document would show the transfer to you and the date.