How to migrate users from Win2012R2 PDC to SAMBA BDC?

Question

Active Directory

Good day.
I came to an office where there are no licenses for Winserver and the management does not want to buy them, but it works as it should ...
They use Windows 2012R2 as a PDC
Moreover, the GPO is practically not used, the rights to 2-3 balls are distributed in the simplest way.
In fact, the functionality of SAMBA as a PDC / BDC is enough.
When trying to transfer users to SAMBA, problems arose.
Apparently, samba cannot fully take on the role of AD DC

Lack of support for domain controllers based on Windows Server 2012 and Windows 2012 R2 together with Samba as an AD DC;

And if I raise 2008R2, then transfer the PDC role to it, bring out 2012R2, and then take the AD DC roles from windows 2008R2 with SAMBA?
What kind of rake can I stumble upon?
I plan to use Zentyal
I will be glad to any answers.
Please do not kick hard and do not offer to leave an employer who does not want to purchase licensed software. Crisis, no work :-(