Legal Question in Family Law in Montana

The best answer is, "It depends."

If Father is willing to allow the children to move, the simplest thing is to file a Stipulated Amended Parenting Schedule that reflects Father's permission for the children to move, the anticipated parenting schedule, and child support based on the new parenting time-share, travel costs, etc. If Father is taking only 10% of the parenting time now, about 36 days and nights, you might not need to recalculate child support (especially if if you meet half way to deliver and pick up the children).

You will need to show the court that moving the children is in their best interests. Among them is that Father is not taking advantage of his parenting time now, so stability and continuity for the children is best served by remaining with you when you move to WA. You will need to show the court what "stability" looks like now and what it will look like in WA.

If Father's child support has been unreliable, your steady income is in the children's best interest. If your best employment offer is in WA, your income will alleviate the stress of Father's unreliable financial support and will provide a higher degree of financial security for the children.

At this point, I would leave the new relationship out of the mix unless you and he are working toward permanence, e.g., getting married, getting a house suitable for the new family, etc. You should show the court your ability to support yourself and your children, independent of another person's income, and that you can provide stability and continuous care for them in WA.

You mention being separated for two years. You should finalize the dissolution of marriage while you still live here, if only for convenience. TYour parenting schedule should provide for long distance parenting schedule, where you and Father will meet to pick up the children, that each parent will be responsible for his/her own costs of transportation assuming the location is equidistant, telephone contact between dad and the children, etc.