I support families moving overeas, and therefore often to a new education system.
The advice I would give a family in this context is don't move.
That sounds really hard, but you are moving to another system at really key moments in your kids education. This is huge, I cannot overstate what an enormous thing you are asking of your kids.
It may be the make or break with results and especially for medical applications.
I understand that Dad has to take this job, so the best way to mitigate the move would be one of these:
The one taking GCSE this summer, they move this summer. Very important point someone up thread says about starting next syllabus in June/July so you need to check out if they need to go into school after exmas in June. That in itself is pretty tough, to finish exams and not get a break. Scottish school year begins in August too.
For the next one down, this is pretty awful. I think I would be looking really hard for a way for them to stay in current school until end of next year.
If they do move to scotland, you need to look more closely at the system. They would probably do better to repeat this year in the scottish system, so they start the curriculum again. Is that possible? So many curriculum differences may be there, that they will not be able to jump in half way through.
If it is not possible to wait the 2 years, and it is not possible to repeat the year, then the sooner ds moves the better.
If you wait until July 2026, after ds has done GCSE, then I would seriously consider leaving the oldest to finish their last year of A levels in their current school. Is there someone who would consider taking her in as a term time 'lodger' for that year?
If they were living with a friend or relative, then they oculd finish their A levels there.
As a teen, my familiy lived apart, Dad worked in Scotland, Liverpool and Birmingham over a period of about 6 years. Mum stayed put and I went to school where she was. It was hard. We did long distance weekends and half terms/holidays, but they knew that he would not be in one place long, and the school stability was more important at that age.
It sounds hard, but moving to another system is harder for your kids.
Probably I would opt for:
Dad starts job.
family stays put until July 2026. Then most of family moves and oldest stays put for last year of A level.
I think you need to plan to travel to Inverness over Feb half term and visit the school and talk through the differences and the timings. And ask how much they can accommodate/ help etc.