Toddler Sleep Changes and Unhelpful Husband

[ECL3]

Hello
New here.
Can anyone help with a toddler sleep change issue along with caring for multiple children.
I'm 5m postpartum with DC3 but since 2 months before birth, my now 2yo DC has gone from sleeping relatively well when not poorly to waking every night, several times a night. He's also gone from eating well to only sometimes having 1 full meal in a day, sometimes 2, rarely 3. It's like he wants it but can't have it.
My DH had to 'start' parenting when I was 8 months pregnant with DC3 to cover the time I was in hospital / complications I had after birth (slightly extended stay in hospital). He never really parented our other 2 prior to this so life hadn't really changed for himsl, it's just been me as we don't have any family help.
My DC2 has had this bad sleep pattern for 7 months now, but as my DH is the one responding to him whilst I'm staying with baby downstairs (so that any crying doesn't distutb the other 2 xhildren), I find DH getting more aggressive in his tone because he's tired and not used to parenting / going to them.
I'm drained but starting to worry about my DC being with DH from bad mood swings.
I've tried a few things to try and help DC2 sleep better, but I'm now starting to wonder if it could be something medical. Any suggestions?
Thanks

DH is a good entertainer for the children, he's just never done the 'caring for them' element of parenting before DC3 arrived. He does come from a very old fashioned household which I think is part of his problem I.e. he was an only child (his mother had a still birth after him and didn't want to go through the possibility of that happening again). His mother was also a stay at home mum whilst dad went out to work, etc. He never cleans up after himself as an adult either, I felt I had to remind him that I'm his wife not his mum a lot, I go out to work (now part-time) when not on maternity leave which I am in now.

DS2 bedtime behaviour changed towards the end of my pregnancy with DC3, even with me going to him. We do the same thing, calm him to let him know we are there and then sit outside his room for a bit. It's hard for me to be in 2 places taking care of baby as well, hence DH having to help now. Baby has chronic reflux so has to have smaller feeds more often, including a dream feeds to keep his feed levels up followed by holding him up for 30 mins after feeding.
DC1 is 7 so in full-time time school, DC2 is such a happy little bouncy thing by day and goes off to sleep well, just had trouble through the night. DC2 does go nursery twice a week. DC2 also stopped napping around 4 to 5 months ago too. DC2 is tall, has been in 3-4years clothes for a while and only turned 2 on November. Still in a sleeping bag in a cotbed at night, perhaps he needs regular pj's and bed now? He just seems so 'young' still, but tall. He has all teeth apart from 2 of the very back ones, so it's not teething but he does also have very soft poop. No whirring gas noises I'm his tummy or rashes to go with the very soft poop (poop consistency used to be firmer but changed to very soft about 4 to 6 weeks before his sleep quality changed).

His bedtime behaviour changed at the end of pregnancy because he could sense change. Then the awful change did happen, his primary caregiver was no longer available for him, then he was replaced by a new baby. I'm not sure how you can't see this. He needs you back. Why can't DH look after the baby while you settle DC2?

I can see it, hence asking for suggestions.
DH is a shift worker, irregular shifts patterns as well, so I need to do a much at I can fit all the children.
Health visitor not helpful, just says DC2 is growing well, developing, etc, so not concerned.

You are asking for suggestions, but haven't mentioned that you have tried putting DC2 to bed. I would also suggest trying to have some one on one time with him to make him feel more secure again.