Q: Father and sister are joint owners, both in deed, but dad pays mortgage. What happens when he dies?

A: It depends on what the deed says, and who has actually lived in the property.

A: Sister owns house but house encumbered by mortgage. Depends upon will, but if she doesn't pay mortgage, the Estate is going to be embroiled in a Foreclosure battle, which no one wants. Here is a good article.

http://homeguides.sfgate.com/happens-mortgage-mortgagee-dies-43271.html

A: The mortgage is a security instrument entitling the holder to foreclose on said security interest in the property if the terms of a note (loan) are not paid. If your father is the only one on the mortgage and his estate stops paying then the bank can foreclose on his interest in the property, similarly if both of them are on the mortgage they both have to pay otherwise both of their interests can be foreclosed on. There are different types of joint ownership the two most common in this instance are "joint tenants with rights of survivorship" and tenants in common. If JTROS then when your father passes away your sister gets his 50% automatically and still has to pay the mortgage. If tenants in common then your dad's 50% interest (or whatever percent he may own) gets passed down to his estate (whatever it says in his will or if he dies without a will [intestate] then according to the succession laws in the state in which he passed away or where the property is located.