Updated: I have sole physical and legal custody. Does that carry more weight?

In my marital settlement agreement I got him to agree that in the event of my death, the custody of my children would go to my sister. The reason being family continuity.

The father is seriously in arrears and in the past 2 years he has only seen them for 7 weekends. He talks about how they are his priority but has shown otherwise.

I would like to ensure that my wishes are followed in the event of my death. I would like my sister, or my other siblings in the event something happened to my sister, to have custody of them, with the father keeping his visitation and support as they are. To my sister or any one of my siblings, I know it would not be burden and my children would be raised the same way I would do it. What I don't want is for my children to automatically go to their father. He would pass them off to his mother or sister. For them, they would do it, but it would be a burden and financial hardship, which they would never admit. It would be a totally different and restricted environment for them and they would be living in a different city and would immediately lose contact with my side of the family.

Is my MSA enough? Can I write this in my will? What are the words that I need to include to ensure what I want is respected and considered by any judge? Is there some other legal document I should have?

Specify in your will who you want to have custody of your children in the event of your demise. But I have to warn you, regardless of what you may specify in a will, if something were to happen to you, the father, if he wants it, would stand a very good chance of getting custody over your sister or anyone else.

I have sole legal and physical custody. Does that carry more weight?

As long as you're alive having sole legal and physical custody matters a great deal. However, courts tend to look toward the other biological parent when one dies. As said before specify in your will who you want to have your kids there is always a chance that your ex won't contest it and if he does the judge will decide where they go.

No, sole legal custody and physical custody does not carry more weight at your death, since at your death, that custody ends, it matters greatly now, in the end, his rights are not taken away, so once you are dead, the only person with any legal rights on that child will be his.

If in the child custody agreement, not divorce settlement, he agreed to allow this person to raise the child at your death, that adds more weight,
But at your death, he can still as to have that over turned and try and get full custody.

In the end there is little you can do now,

But you can specificy who you want and should, and then be sure to leave them enough life insurance to cover a court battle over child if it ends up that way.