Tell him that it's a great idea and that he should practice by doing all of the childcare over half term while you go out and do things for your mental health
Excellent plan!
And not just the childcare! Being sahp is NOT just childcare he doesn't get to leave all the chores and life admin to you if you're the one working and he's at home.
Too many of THIS type of man who chooses to be a sahp cos they think it's a total doss do the bare minimum of childcare (feed the kids crap, plonk them in front of tv etc) and do NONE of the associated work like dishes, laundry, general tidying etc there are several threads like this and the mum feels unable to split as they fear he would get residency
I've seen it a couple of times irl too.
This is NOT to say all Sahd are like this I also know and know of others who genuinely step up and put the work in but I REALLY don't see this guy doing that.
Given what you say of his attitude at work as well as at home (not one night waking the whole summer holidays?! Wtf!) he sounds plain lazy!
I'd even go as far as to say if you can afford it and feel you can do it emotionally, and despite his laziness feel confident the children wouldn't genuinely suffer - go away for a break next half term, or even just a long weekend (inset day?) throw him in at the deep end and don't let him off household duties either on this coming back to a home that's a mess if you did this would be totally unacceptable! At least the older one if not expressing for the younger.
I agree @Classicblunder I think he'll make a pigs ear of it! But it may be enough to put him off his grand plan of not bothering with work cos being a sahp is sooo much easier  (and yet he can't even settle them on one evening? Aye right!)
@LookItsMeAgain yea I agree when I had dd I planned to be an easy going not routine led mum and I ended up with... a baby that craved routine especially around sleep/naps and feeding times - and if we didn't stick to that it was murder for all of us! Even my ex recognised and accepted that. Much later in dds life (she was nearly 12) she was dx with a disability and I later learned that this is common with babies/children with that condition as they have issues with fatigue, pain and digestive issues. She was doing naturally what was best for her body.
I've also been a nanny and childminder and every child is different. Some don't need or want a routine, others it's essential for them, most are somewhere in between.
@LookItsMeAgain the difficulty with the driving test is there's a huge backlog due to COVID and tests weren't happening during lockdown. My dd and her friends are at the age/stage of learning to drive and local Facebook pages too I've noticed it's incredibly hard to even get theory tests booked. 6-8 month waiting list here and that's not even to get a test that's actually local that's in glasgow which is about an hour away by train from me - this is the other issue the THEORY test centres are sometimes not convenient/easy/cheap to get to for those travelling by public transport (which of course many of those going to these places will be! Utterly stupid in my opinion not to have them somewhere central or at least one of them!) practical tests it's about 10 months!
He cannot sit like a waif on the landing saying "It's useless...I can't do it". That is not an option. He has to persevere with it. He hasn't a clue where the kids are concerned.
Yep! We see this so often on here and again I've come across it irl too (in particular as my mum recently reminded me, one relative by marriage would give it "but the baby/toddler won't settle for me" my dad lost patience with him one time and let him have some home truths "well maybe if you were home more (golf fanatic) and DID more bedtimes that wouldn't be an issue! It doesn't happen by bloody magic! Your wife didn't instantly know how to settle them she learned what worked for them by doing it every night! That's what it takes, time effort and practice" relative made a little more effort after that for a while but yea basically lazy and entitled - which is so often the case with men like this.
I’d start making notes of times and dates when he can’t handle the kids. Like you having to leave a work call to do bedtime
Yep this could be useful come a potential split
I suspect even if you split he wouldn't even go for 50/50, I think he is just basically lazy and would rather not work and not have any responsibilities at all. But I get why you're worried and feel the need to protect yourself in case he did try for residency or 50/50 but I reckon he won't bother