Legal Question in Real Estate Law in California

It depends on the priority of the tax lien. If you owned the house before the lien, your 1/4 is clear of the lien. They can theoretically execute on the lien and sell her 3/4, but they'll have a hard time finding a buyer, because the buyer at the lien sale would become co-owner with you. Not many people would want to buy into that situation. I suppose an investor might come along, buy 3/4 and then offer to buy you out.

It would be helpful to know how you hold title.....are you joint tenants or tenants in common? If you are a joint tenant, you would succeed to 100% ownership upon your sister's passing. Otherwise, her 3/4 interest can be passed on by her will or trust, or absent these, by the rules of intestate succession. Now, as to the property tax situation. Whether or not your 1/4 interest is clear of the lien, things will get very messy when a lien sale takes place. I think the common-sense thing to do is to step up and pay the taxes. As a co-owner, you are entitled to do this, and technically, the amount that represents your sister's share becomes her obligation to you. You have a lot more to lose (a potential inheritance??) if the house is foreclosed than the taxes you'll be paying.