XH and I had mirror wills, obviously had to make a new one after the divorce. I appointed my mum and cousin executors and also my cousin as guardian of DD. That doesn't mean anything though as if XH wants her he will get her as the other parent. But I did ask that he appoint my cousin as her guardian in his will, so if anything happens to me, then him, that my DD comes back to my family to be brought up and he agreed with that. It also means that he has somebody from my family to watch out for DD and to discuss issues with. Although he probably wouldn't, as he is an arse.
Mum and cousin are also financial trustees of the will, so that they control the money, so that if DD goes to live with him, he cannot access it and blow it (he has form for debt). (there will only be money if I die, due to life insurance to pay off mortgage etc, there's no money now).
It is not a nice thing to think about, however, it needs to be done if you want to secure your DC's future. Mine only cost about £80, so it doesn't have to be expensive.
A solicitor did tell me that if he didn't see DD for several years, then I died, that it would be up to my family to fight him for custody, she might not automatically go there if he hasn't seen her for years.
He has picked her up today for the day, the second visit this year, and agreed to see her again in 3 weeks. Little steps.....