Indenture papers stating joint tenants with the right to survivorship ?

Yesterday I received a notice in the mail from my father who I haven't talked to since I was 16 stating that I had to pay 1/3 of a new sewage system in his house because I was considered a joint tenant. I guess when I was 16 my grandfather and my father added me onto the house as a joint tenant with the right to survivorship so if they died I wouldn't have to pay taxes. The indenture paper states Mr.----, individually hereinafter called the grantors, of the one part and then states all three of our names and lists us as joint tenants with the rights of survivorship hereinafter called the grantees of thR other part. My question is do I have to pay 1/3 of the cost or not?