Moving from Scotland to England- what school year?

[NellNorth]

I have googled this, but I want to be sure, and would really appreciate any insights.
My DH is self employed, a contractor, and most of his work is in the south east. The family have remained in Scotland, and he has commuted. For various reasons, we’re contemplating a move south. We will be selling up a large family home, with a view to living in a much more modest house, well outside the M25, pretty much mortgage free. We’ve lived down south ( pre kids) before, so we know the areas we’d focus on.
I’m not British, so I need a wee bit of help with the education system.
DC1 dob Sept 2005, age 14, current in S3,
DC2 dob March 2007, age 12, currently S1,
DC3 dob Sept 2009 age 10, currently P6

What years would they be going into next Sept? And would DC1 be doing state exams the following year, in summer 2021?
I’m assuming that the curriculum in Scotland and England will be broadly the same- do you think that’s correct?
We’re also keenly aware that Uni is free in Scotland to Scottish residents, so we’re weighing all this up as well.
So much to think about!

I think:
DC3 - current Y5. Y6 and SATs next school year.
DC2 -current Y8, Y9 in Sept.
DC1 - current Y9, y10 in Sept.

DC1 would just be starting GCSE courses. Exams at the end of Y11.
GCSEs are a 2 year course. You really dont want to be moving later than Autumn 2020, as DC1&2 will be caught in 2 year courses for a while, with limited opportunities to move without pretty significant disruption. It is possible to move during GCSE or Alevel courses, but not recommended.

In England we have 7 years of primary school but labelled Reception (like your P1), year 1 (your P2) etc.

So P6 is year 5 in England. S1 is year 7 in England.

Thank you both for replying. It is really makes everything clearer. My middle child will effectively skip a year of secondary school, I think, going from being a current year 7 equivalent in Scotland, to a year 9 in England. That might be painful!