"I had planned to sell my parents homeplace as it is vacant for 1 year now."
Its not clear but is it the case that your parents are dead? If you were selling would it be as executor or beneficiary?
Have you asked him about selling? Have you given him the option of buying out your interest? That should be your starting point.
In general & in theory, you are entitled to sell. However, if his signature is necessary, how can you force him to sign anything unless you seek a Court Order? Try to avoid that unless of course there is no other way.
mf