He has always been fairly reasonable about his salary and we consider it a joint income until it comes to big purchases, then he makes the decisions.
This is not reasonable at all. He is financially controlling. He's only ok with you spending money if he agrees with what it's spent on.
I want a passport and I want to be able to take the kids somewhere
Then get a passport. And for the DC.
As usual my DH has demanded ‘why do we need them
You're being financially controlled. You don't need to justify spending decisions to him, unless it's something big when it should be a joint decision. Just get the passports and stop asking permission for these things. It should not be an issue. It will be, because he's financially controlling. Watch your back. When you start standing up to an abuser, the abuse often escalates into violence. If you can, get the passports using cash and don't tell him you have them, because frankly it's none of his business whether you have a passport or not. If he never takes DC on holiday he doesn't actually need to know that they have a passport until the time comes that they want to use it.
told us he can’t afford them.
This is bullshit, as you're well aware. He's not broke. Even if he was, it could be your Christmas and birthday presents all joined together for one year.
He has told me yet again that I don’t need a passport
He is wrong. You want to go abroad so clearly you do need a passport.
What he's saying is that he doesn't want you to go abroad and will try to prevent it, which he is doing by denying you a passport. This is controlling behaviour. You have the right to go anywhere you want.
Obviously you'd discuss it with a husband and not just randomly disappear one day and call him up announcing you're on holiday. That would be unreasonable. But if he tries telling you you can't go on holiday, then he is being unreasonable.
The discussion would be around:
When and for how long (eg don't deliberately book a holiday the week your partner is attending a dead relative's funeral or eg the weeks before/after your partner is due to give birth. Those would be unreasonable situations).
What's happening with childcare (if you're usually the childcare) eg if he needs to do school runs that week then he needs to know this, and you'd need to find out whether he actually can do it or not with his work commitments, if not another solution would need to be found or else don't go in holiday that particular week.
Where are you going (so he knows for emergencies) and contact details for the hotel, flights details so he can pick you up on return if you need that, unless you're planning to make your own way home.
Any concerns about whether the country is currently safe to travel to (wars and political unrest etc).
He has a say in whether his minor DC go on holiday or not and where. But with no good reason to refuse, he should agree, it's not ok to be a controlling arse with DC any more than it is with adults. Having the final say because you're a parent and considering the DC welfare and what's best for them as well as family finances is different to being controlling, you'd need to ascertain which it is before you could say whether he's being unreasonable or not.
Eg my family couldn't afford the school skiing trip, that's not controlling to say DC can't go.
It wouldn't be controlling to say DC can't go on holiday to Gaza next week, because it's at war.
It's not controlling to say DC can't go on holiday with X friend and friend's parents because you've never met them and can't be sure they'd keep DC safe, that would more be a personal parenting decision whether to allow it or not and people would have different opinions on it, as married couple you'd have to both agree.
It's controlling to say 18+ DC can't go on holiday because "my house, my rules".
It's controlling to say you can't take DC on holiday yourself, when there's no question of your ability to be a good parent.
It's controlling to say DC can't go on holiday with you to visit eg your parents in your home country, when there's no risk of you abducting them.
That ⬆️ sort of thing. He doesn't own you and doesn't get to decide how you spend your free time. The fact he's trying to is very bad news and means he's trouble. You should consider divorce. Controlling partners aren't safe and healthy people to be around.