OH wants me to leave PT job to work FT....

You need someone who is going to make him see sense. You are doing enough as a mother and wife. Contributions depend on how much time we have and how much resources we can attain. The best thing you can do is perhaps try couples counselling with him involved.

I think you are getting a hard time OP. If I read this correctly, you've only just moved to this arrangement as you previously had twins on the days off and they only just started school - after having all childcare the entire summer.
Im not buying that he's stressed. Saying things like he'll sell the house and sign on are bullying behaviours.
Are you married to him? If not you may have major issues ahead.

I'm still really confused about the volunteering. Are you saying that you did the volunteering on the days you were also looking after the twins eg whilst they played? Or is this something you have taken up now that you no longer need to look after the twins?

And were you going to request more days' work from the company or just higher rates?

He's handling this all wrong but is there something happening with his business that has worried him about his financial responsibilities? Could you drop your volunteer day and maybe get some evening tutoring work, just to bring in a little more money? Perhaps his and/or your mum could do some before or after school childcare just to enable you to pick up a few more hours. He seems to be ignoring the work involved in looking after 4 DC, even once they're at school.

Part time jobs with your hours and term time only are like gold dust. If you leave you will be highly unlikely to find another like it and with 4 kids childcare before and after school and especially in the school holidays would be astronomical.

You would basically be doing the extra hours with little if any financial improvement. I doubt a 73 year old grandmother will be willing or able to have all 4 kids every day, especially in the school holidays and if this fell through you wouldn't have any job at all. You are not a part time worker op. 3 days at paid work plus all home responsibilities with 4 kids is very much a full time job. It's a pity your DH can't see that your current set up is pretty much ideal for the present and you have a plan for the future.
His life and your children's would be impacted quite negatively if you both had to work full time with all that you do being fitted in at nights after work and the inevitable anxiety regarding childcare in the school holidays and who has to stay off when one of the 4 children gets sick. Plenty of people are stuck on this exhausting hamster wheel and would love to get off it for a scenario like this with some work out of the home and more time with the children as well. Don't give up this amazing job which fits around 4 children until you yourself feel ready. 💐

Up your tutoring immediately to 5 days a week or do it on the weekends instead of afternoons. Housework can wait or DH can do some of it. It looks like you planned your life around kids and housework the way you wanted and refuse to change it. Your DH is screaming for help. Kids will be fine. Are you in debt, financial troubles, etc.? Something must be going on if he is frustrated like this. If tutoring pays min £12/h you can earn at least 1500 per month by working 5h/day 5 days a week + 8h on a weekend. After that, in a years time, you can start your FT job as planned and earn your 2500 that will pay for childcare.
Seriously, 2 days off paid work is a luxury and not many people can afford this.

He’s a bully.

Yeah he's a twat.
What's he actually going to do to facilitate you working full time?
Is he going to do the school pick up and drop offs or contribute to paying for the before and afterschool clubs to cover that?
Is he going to take up half the housework or contribute to employing a cleaner?
If he expects you both to be working full time he needs to pull his weight with the children and the house
Don't put up with this bullshit from him.
Either he makes realistic commitments to stepping up or you remain working part time so you can also do the household tasks and childcare.

I'd move to tutoring 5 days a week till school pick-up, plus say 3 evenings a week. If that's not enough, maybe a Saturday morning with DH looking after the children.

I just feel stuck and unsure how to achieve what he is expecting.

Can you afford couples counselling? Maybe he needs a third party to ask the questions about what happens to the children. Or to get him to open up to you about what's behind this sudden change of mind.

Why are you not tutoring five days a week? As others have pointed out, a day volunteering and a day for housework is a massive luxury with four kids and a DH who sends course to burnout.

He works very hard, long hours/early mornings, I know he is feeling burnt out.

He's being irrational about the ramifications and the childcare is your get a different job, and he's communicating horribly. But work stress like this led to my late husband having a full on breakdown, from which he never recovered enough to work again.

You're being unreasonable to spend two weekdays earning nothing, when your DH is feeling massive financial responsibility and working all the hours god sends.

Aim for a compromise and say that you'll do your present job five days a week until you can apply for the job you want. And for goodness sake put up your rates. You should easily be getting up to that £2k if you tutor f/t at the usual rate.

So funny how many people think it’s a gotcha moment to ask him what he will do about school pick ups and house work, plenty of parents work full time and manage housework and childcare. The husbands of mumsnet must be absolutely shite if so many women are convinced that because he’s at breaking point being the main earner that must mean he wants OP to work full time and do EVERYTHING. She’s not said that, so are people basing these assumptions on their own husband?

I’d call his bluff. But id mean it. It’s time to have the “talk” op. He wants parity, split. He has his children 50% of the time. As do you. You will find that with 50% of your time childfree and without the logistical worry of them that you can get a “proper job” and “earn”. As to his earning now that he has to consider his own children - it may take a hit. His extreme stress is unlikely to lesson tbh. He’ll probably find it a fuck ton harder. But oh well. He wants parity? Equality? Fairness? As do you! So he takes his half of the parenting. You take your half of the fiscal responsibility. But you can’t pick up the financial slack on your side whilst he fails to pick up the parental slack on his.

Clearly they should share all the housework and school runs. DH and I always have.

“Ok, can you write down which chores you will be taking over and when. Also which school drop offs you can do. If we can sort the logistics so it’s fairly evenly split and workable, then of course I can start applying. It’s the logistics I’m worrying about”

I’m sure there is something going on at work for him to change so drastically. Can you persuade him to open up?

If you were to work 5 mornings per week term time, that would be a compromise that might work. You don't need a day off to do housework if you are home at 2ish. You have every afternoon at home. That's what I do and there is plenty time to do it all plus afternoon activities for kids. It's busy but doable. I agree the volunteering is a bit indulgent, from his perspective. You could park that for a year or two when times are toughest and kids are young. If he is already burned out he wouldn't be able to cope with the massive additional workload for him if you go full time. He needs to understand that, he possibly doesn't realise. He is being horrible now but I think he needs a few days off to unwind and see logic here, he sounds in a bad way.

You could easily make this work. Tutor in the evenings and he'll do the housework and childcare like he said. That makes your hours up to full time.

I agree with this.

Just seen your update, he is being an absolute arse.
He is in the wrong not you.
He should respect the contribution you are making.
The grass is always greener, does he ever look after all 4 DC by himself?

You could work 'full time' providing it's within school hours, however it's not that simple is it? I'm a tutor and you're lucky you've got so many daytime hours. I work evenings and weekends which can be a nightmare for childcare when my OH is working late.

Your OH isn't really thinking this through, and I imagine he's simply taking the stress of his job/pressure of being the breadwinner out on you. You need to come to some kind of compromise which would take some pressure off him but also work for you and your children.

People say drop the voluntary work but I imagine that's investing in your future role by having it on your CV. Does it need to take all day? Perhaps drop the housework day, pick up some extra hours tutoring if you can and you both come to an agreement to catch up on housework evenings and weekends.

What are your finances like? Are in struggling, in debt? Or managing fine?

Working full time with 4 primary aged children is an absolutely massive ask, especially if he isn’t pulling his weight too.

In what way is this a "half way solution"? When will the housework get done? By whom? What is the OPs DH doing in your scenario for it to be half way?