Glad the chat with FIL went well. It sounds entirely credible that SIL is rushed off her feet. As more and more workplaces are opening up now I think a million and one non-urgent jobs that were shelved during the lockdowns are having to be dealt with.
Don't doubt yourself, MoreLegs, it shines through your posts that you are a nice person. And, as I've said before, it would take an extraordinary level of spin to whitewash H's behaviour.
He may have been a good father when the DC were little but it sounds as though he got bored with the role when they grew older. Parenting teenagers is harder work in some ways than simply caring for the physical needs of cute, tiny kids and cuddling them a lot.
So I also suspect you've been doing the job by yourself for much longer than you thought. The way the DC have reacted does not indicate that one of the main props of their lives have suddenly been withdrawn.
I think a lot of loneliness is in store for him. I don't say it to gloat, but just because I can't see how you can abandon everyone who cared for you and not end up lonely when you reach the stages of old age and failing health. He's put all his eggs in one basket and it's a very rickety one.
I hope the weather's nicer where you are. It's grey and damp here. Good for the garden but annoying when I was planning to go out and tackle the host of dandelions that has appeared.
Someone said - I don't remember who - if dandelions were hard to cultivate how much we would value them for their beauty. And it's true, they are lovely, both as cheerful, sunny pompoms and as graceful, fairy-like clocks. Only, they're invasive thugs so we stop noticing how beautiful they are. I often think of that saying as I'm struggling to dig out another mile-long tap root.
I hope today's a good one for you MoreLegs. Take care. We are all rooting for you.