Legal Question in Family Law in California

Without knowing both WA and MA law on the subject, I can't give you a definitive answer, but if they follow most states, WA will decline jurisdiction being neither the location of the original proceeding nor the location of the minor children. Because neither ex-spouse nor any of the children live in CA, however, CA should surrender jurisdiction and MA should be willing to take jurisdiction readily. You can try filing in WA courts and see if CA will surrender and WA will take it. How likely that will be to succeed you will have to ask a WA attorney.