At this point can he/you as a family just take holidays in sunnier places till kids finish school? Most people do end up doing something along those lines.
I wouldn’t move again if you’ve got a job and kids are settled in schools and some or all of you speak the language of the place you currently live in.
The reason I’d really emphasise this is that your eldest has just started secondary. An educator (not mainstream!) said to me that up to age 12 the major influence really is the family beyond anything else such as school and peers.
I definitely found that to be true. We lived abroad and moved a bit and were quite maverick wrt education till our eldest was 12. Sometimes that meant paying too, even though we were both state educated and not intrinsically in favour. Paying for kindergarten till age 6 rather than start uk school at age 4, for a ND child who didn’t seem ready, for example.
But from when our eldest was 12 to when our youngest started university we did prioritise their ‘formal’ education in every family decision. A period of 10 years.
Both me and DH had flights of fancy during that period - for sure - due to our natures. But we had to find other outlets, and to a reasonable extent that did work.
It just seems embedded in your DH so it won’t change but he has to find a way to work with it/around it somehow, without pushing the ‘next move’.
Hopefully he’s more resilient on this issue than he realises if he previously managed 10 years in the uk where the rat race and weather are bad!!
But underlying all this is there something about leaving his home country at 18 that he needs to address? In a way that doesn’t involve uprooting everyone? So young