@MintyCedric and @5128gap probably have the measure of this - your daughter may not even realise quite how horrible her H is being, she may know full well but have decided she doesn’t have the energy to change things with a preschooler who gets seriously ill and an older child to deal with…
I would deal with your feelings about her H on your own - do not judge her for his behaviour. At the very most, when things are back on a more even keel, you might want to express that you’re sorry she felt she had to lie to you about why she needed the childcare help while her littlest was in hospital, because you’re there for her if she needs support for any reason.
Be there for her as much as possible going forward. Offer a listening ear, ask how she is feeling, most importantly LISTEN to what she is telling you and leave space for her to talk if she wants to. No-one wants to confide if they fear being judged or told what to do - it’s not always simple.
Does your daughter work outside the home? If not I’d use the next year or two, before the youngest starts school, to encourage her to go back to work when the youngest is settled in reception. If you are in a position to help make that easier with school pick ups etc then do what you can on that front.
Her H sounds entirely selfish at the very least, and the more independence she has, financial and otherwise, the fewer barriers she will have in future to leaving him.
I really recommend you read the book Why Does He Do That? by Lundy Bancroft (you can download on kindle app/Apple Books or get a hard copy second hand). It provides an incredible insight into the impact of being with an abuser of any kind. It also makes the very valid point that telling someone in that situation what to do isn’t necessarily the best way to support them - they are already being told what to do and having their own empowerment eroded enough within their relationship.
I hope your grandson is better soon. 💐
(Might be nice to invite her over with the children for an afternoon when they get out of hospital - or offer to go over and mind the children so she can have a nap. Doesn’t sound like the kind of thing her H would do for her…)
Be better than him and provide her with support you’re able to. NO JUDGEMENT. She’s your priority - don’t waste energy on him.