Legal Question in Real Estate Law in Washington

If you want to force the name of one sister onto the deeds, then yes, you need to go to court to seek a declaratory judgment, which means, you are asking the court to find that the unnamed sister is in fact an owner who belongs on title.

I imagine the matter is going to be far more complicated given the passage of 30 years since the property was originally purchased. Forgive me for being cynical, however I am usually dubious when someone tells me that 100% of the family is behind the unnamed sister, and it appears the only person against the unnamed sister is the sister who is in fact already on title. Unless the rest of the family who are willing to give statements were there and saw the purchase 30 years ago, their statements carry very little meaning or weight when it comes to determining whether both sisters purchase the property at the same time and both sisters were meant to be on title but for some reason only one went on title.

Best of luck to you.