Appletree my DH was a SAHD for 5 years - sometimes during those years I worked full time, other times part time, so I know where you are coming from to some extent.

So three things spring to mind immediately:

Firstly, children are generally way more flexible than we give them credit for. We may think they need a nap at 9.30 each day in their cot with their blankie, but the same kid can (eventually) happily sleep at 10.30am on a baby couch in the lounge. They will eventually get used to "when mum is here we do X" and "when dad is here we do Y".

Secondly, there are some things your DH will do differently to you. Sometimes his way will be better, sometimes your way will be better. Sometimes you will never agree and the kids will just get used to different ways of doing stuff.

Thirdly, there are some things which are "not negotiables", like giving toddler formula to a 10 month old. Put your foot down over things like that.

As for everything else - phew! It is really hard trying to negotiate the shared parenting juggle! You probably feel like he is criticising you, but I suspect you are criticising him too? (the title of the thread is that he is "mucking it up"). It is so easy to do this, I understand how it happens The only advice I have in that department is to try and bring up the whole "issue" when you are both in a really good mood and pepper your statements to him with as much "I love how you do X with the kids, I think I will take that on board" as possible.

I don't really know if writing a plan would work just now - your DH might see your suggestion of writing a plan as a way to control his time with the kids, which just might make it more of a battleground. Maybe try it once things settle down and you both feel less attacked?

HTH