Security groups and default access

Hi. I want to create a new customer, and under that alot of RDP connections to the customers server.
But i want to make shure the security is right.
How can i set up that only a security group can see / access the rdp connection / customer
Can i do this for the customer and all the rdp ore is it by connection
and if we have a 3. party that needs access to management, but only 2 server out of 10 under the customer, how can i set this

best regards