Is it possible to change joint tennants in common with rights to surviviorship

First, I'd like to explain that there is no such thing as "joint tenants in common with rights to survivorship." There are two forms of joint ownership in Georgia: one is "joint tenants with rights of survivorship," and the other is "tenants in common." The difference is that a parcel held as joint tenants automatically passes to the surviving owners at the death of one owner, while a parcel held as tenants in common does not. Instead, the interest held by a deceased tenant in common passes to his probate estate and can be controlled by his Will or intestacy if he has no Will. Second, your father needs a Will to control where his property goes, not a "living Will." A living Will is a health-care related document, and Georgia doesn't even use a living Will form anymore. It was made part of an Advance Directive for Health Care in 2007. A regular Will (or "Last Will and Testament") is what your dad needs to direct what happens to his assets at his death. As to the actual question: your father has been making gifts to your sister every time he pays the mortgage or other expenses, and he made a gift to her of her 1/3 share of the down payment when he made it. He's also been making gifts to your mother, but those likely don't have gift tax consequences. Your sister is a real owner of 1/3 of the property, even if she never paid a penny, because her name is on the deed. If she is willing to sign her interest back over to your parents, then they can have her sign a deed (preferably either a limited warranty or warranty deed, and not just a quitclaim deed) and give her interest back to them. She's making a gift at that point. If she's not willing to sign her interest over, then they'll have to try to buy her out. Your dad should consult an estate planning attorney as soon as possible to discuss options and figure out how to move forward.