OPs other half is in a committed relationship - it's just with another woman and that is the entire and total crux of the matter.
That is the thing that needs sorting out first and foremost (aside of course from the will and all that side of things which I'm so glad is now getting looked at).
It's got to be virtually the near 100% break that most people have when they split from their previous partner, divorce or no divorce being involved. Most people want either nothing to do with their PP if they were a particular git or if they just drifted apart and decided to divorce, they'll keep the peace and be civil. But it would highly, highly unusual for the type of relationship that these two have to exist - it's extremely unhealthy for everyone concerned, and I mean everyone, you, him, her, his other kids, your DD. Everyone.
He needs to be willing to relinquish whatever it is that he gets out of being at her beck and call because there will be something that he gets out of it - it alleviates guilt if he was the one to say let's split up (why did they split up did you ever say why or what the circumstances were?), or he gets some twisted 'buzz' out of being bossed around and dragged back repeatedly by the ex even though he probably at the same actually doesn't particularly enjoy it and wishes it would stop.
He needs to end it in all the ways that matter - that will then translate into the switch to the 90/10% ratio that it should be sitting at (in your favour) and should have been sitting at from the moment he/they/she decided not to be together any more and he and you got together and he had a child with you.
Maybe a full on ultimatum from you will give him the momentum that allows him to release himself from this highly unhealthy relationship that he is in.
And I also wonder that if it went on as it is now in the way you suggest (if it didn't all slip back since nothing, fundamentally, has changed and she might only need to have a strop and it all slips back again, who knows), I wouldn't be surprised to see in the future maybe him ending up with a mental health breakdown and then where will you be? How long could he exist under this pressure where he is effectively trying (and failing) to maintain two families at two different addresses? And if you got frustrated and resentful (understandably) and started asking him for a little bit more and a little bit more that could tip him over the edge into depression or worse (that's the kind of scenario I could see as one possibility) - and I say this because it would then present you with a whole host of difficulties - just further down the line.
Have you ever sat down with him and said "What do you get out of it you must see that it's waaayyyy beyond anything normal and that you're her whipping boy" - what does he say? Does he realise that effectively he's being controlled/abused and he's allowing an EX partner to control is current relationship to boot?
It could actually be doing him and thus you and your DD, the power of good if you tell him "These are the terms from two days time and they're non negotiable". It's black and white for him.
God it's such an awful situation and I so feel for you. It must be so difficult and especially at this time of year and looking after your daughter still, essentially, pretty much on your own. The rest of the time you're caring for her, looking after the house - he just comes over a few times a week to play with her/put her to bed? No, it's just not good enough it really isn't.
What's your thinking at the moment after the last few days, how's it going? I have been thinking about you. I've almost posted about three times when you've previously set out the visiting scenario that you've written about for him - it is just visiting not being a proper father (or family member), and it's really totally unacceptable in duration, frequency and honest to goodness genuine commitment. This is almost the behaviour of some of our wonderful non resident dads - not of the parent of the current family that should be the active priority for him without question.
It's one thing that he still wants to do things for his existing children (wish my EXH would do that!!!) but there are limits and his are totally out of whack and highly extreme. It's not normal - you're not asking him to sever all ties with his children, just be appropriate to their need to be independent adults and to be fair to them and to you. Undoubtedly all the running them about is at the insistence of the EXW and just a further extension of her control and guilt tripping.
Your visitation scenario doesn't do anything to bring to an end the weird controlling relationship that he continues with his ex.
I am SO sorry but to me it's still timid half measures/solutions rather than the definitive - "You will do x y and z and if you don't, we're done".
How long can you wait for realisation and genuine insight from him because he's not had a lightbulb moment yet - if getting into the relationship with you wasn't the trigger, if when you got pregnant wasn't the trigger, when his DD was diagnosed as SN, why wasn't that the trigger? He's very likely NOT going to get it any time soon, the current situation will continue and drag on - and on and on and on and this solution is just a sticking plaster to the issue but underneath the wound is still festering - it's called his ex (who isn't his ex).
So awful for you OP and very complicated and tricky unless until I guess you break it down into the one main issue. He needs to not be in a relationship of the type he's in currently with his soon to be ex wife from right now, today.