I feel for you- we've been there too, 'sandwiched' between caring for elderly parents and trying to sort out our childrens' mess. So hard.
However, it does take 2 to tango. Our youngest got herself in a disastrous relationship with a control, macho freak- and moved to the Canaries with him. He was indeed a bar stewart of the worst order- but now it is all over, thank goodness- we can't blame him 100%- she knew how he was, and in some instances I'm sure she aggravated him too. We supported her 100 and more % when things truly went belly up- but we also felt she should take some responsibility herself. Surely your daughter knew he worked away from home and that at this age he would not have as much energy after a long week at work, to care for the children. Sorry if this sounds harsh.
When OH worked very long hours, nights and week-ends, it was hard to look after the house, garden and children single-handedly, with no family support whatsoever as my parents lived abroad- but didn't feel I could expect him to take over when he came home as he was totally exhausted. Not easy- and at times, almost impossible - but then I knew he worked such crazy hours. Knowing I could not rely on anyone, except my wonderful neighbour- just had to get on with it. Sometimes being too close to help is a blessing- but also prevents people from finding their own solutions, perhaps.
Hope it all works for the best in the end. Bonne chance.