Jurisdiction change

My divorce and relocation paperwork were filed in Washington state. I am currently living in California. How difficult is it to have the jurisdiction changed? Both of the children in question live with me (primary) and their father has visitation. I worry that after their father and live-in fiance get married they will try to get custody. She is finishing up her Law Degree on-line (never thought that was possible) and have threatened that this may happen. Any help would be appreciated. Thank you

There is a lot you have left out of this inquiry. If you moved the children to CA without his consent or the consent of the court you could be charged with parental kidnapping...
If the court perceives your moving as a ploy to hinder visitation or in anyway intended to block meaningful relationship of children and father they may consider change of custody.
Do it the right way, go to court and have the jurisdiction changed, most courts will not deny custodial parent from moving the children if done appropriately and with good cause.

Good luck