Communication between DC and RODC?

Question

VPN

Hello,
The main office has win2k8, sonicwall, and the branches have win2k12 and cisco 800-1800.
The offices are interconnected via vpn (isakmp-ipsec). There is also VoIP, 1C, etc. etc. Everything works fine on vpn.
There are currently 5 branches. Each has at least 30 computers. At the main office, at least 60. Portable devices do not count.
Recently there have been problems. Either one employee or another wants access to the file ball in one branch, then in another, then in the main office, and of course the accounts on each server are different.
I would like to change servers in branch offices to RODC mode. Keep accounts only at the main office, so that the branches themselves load what they need. I don't know how to organize. Please help (:
Of course, I looked at several manuals, but everything is vague there.

Answer 1

Set the main Cd, raise domains in branches, enter them into the forest. nothing complicated. I did according to pyatilistnik.org/nastroyka-kontrollera-domena-acti...

Answer 2

I hope branch domains are branches of the main domain?
If yes - then siteing + "secondary" CDs in the field
And as a bonus - DFS - it will just turn out to be a good content delivery "in places"