Does my brother-in-law have claim to a property?

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Good morning,

So I'm thinking about buying a house with my sister. I will be co-signing with her. She is married and the house will be for her and her husband to live in. I already have a primary residence on my own. We live in Washington state (I don't know if that matters).

My question is: if they got a divorce (or she passed), then would her husband have any legal claim over the house only she and I co-signed for? 

Thank you