Firstly sorry for your loss. I would second Winstons Wish, they sent me a great book which helped me explain to DS 7 what had happened to his Daddy when he ended his life.
Essentially what I told him was “Daddy had a poorly brain and none of us knew, Daddy’s poorly brain meant the chemicals stopped working properly and when that happened it made Daddy do something very dangerous which meant he wouldn’t be alive anymore. It is important that you know that if Daddy’s brain hadn’t been poorly he would never have done anything dangerous”
DS hasn’t asked what the dangerous thing was but the advice is to tell him as simply as possible.
The thing that stuck with me was when Winston’s Wish said it’s important to treat mental health like any other illness, like cancer or a heart attack. His Daddy was poorly and that made him die.
They also said to remember that children are very accepting, if you or someone else think you have explained something wrong or could have worded it better you can always say “remember when you asked X? Well Mummy/Daddy/Grandad didn’t explain that quite right, would it be ok for me to try and answer that again?” I’ve done that quite a few times due to well meaning family saying the worst possible answers to DS questions and he’s always accepted it well.
If your children are struggling I’d hugely recommend CHUMs, our assigned counselor has been wonderful and always on the end of the phone if I need help with a question.
Hope that helps and apologies if I’ve overstepped the mark.