Posted below the opinions of Washington licensed attorneys on disinheritance of an issue:

https://www.cliffcoulter.com/post/disinheriting-a-child-in-washington-state

Disinheriting a Child in Washington State - Moulton Law Offices

As both attorneys suggested, it is prudent to discuss your concerns with three/four attorneys in your county.

Once you've done that, retain one to ensure your wishes accomplish what you desire.