GPO - Set RDP access for specific OU Admin only

I have several divisions that have a DC provided to them from the corporate office (Domain "A"). Only the certain PCs at the division access a specific app and need to be on Domain "A" -- the remainder of the PCs are on the local domain "B"

I have created a specific Admin group for each OU representing the division - granting them access to join PCs to domain "A", change passwords, create accounts etc.... only within their own OU.

How do I configure a way to have this OU_Admin group have remote access to their PCs located at their divisions.

I know I can tell them to add OU_Admin group to each PC - but there should be a way to allow them that within AD/GPO.
Thanks