Hello @EarlSioson000 ,
This could be theoretically possible (for example by granting RBAC rights to your users on the Resource Group level, rather then on the subscription level, so your users will be able to create resources only in those RGs you pre-create for them and they won't be able to create new RGs), however, I would discourage you from doing so!
Resource Groups are logical "containers" for your resources (grouping components that belong together, share the same lifecycle). They don't cost anything, you can have up to 980 RGs per subscription, and they should really help you to organize your resources, deploy and manage them in an efficient way. By asking your users to deploy all their apps and solutions in two RGs only, you would make their life much harder. You would eventually bump into some RG-related limits, something you wanted to prevent.
There isn't any direct relationship between your Active Directory and number of subscriptions or Resource Groups you can have, so this isn't a limiting factor. In fact, some customers are "cloud-only" and don't have any on-premises AD, they use Azure AD only (which is a hard requirement, since your subscriptions are "linked" / trust one particular AAD tenant and provide security principals like users or groups to your RBAC model).
It is much better to monitor your subscription(s) with regards to limits (in the Portal or otherwise) and "scale out" (create a new subscription in your environment and onboard your organization / users to it), when needed. You don't pay for how many subscriptions you have, but what resources you provision in them.
Hope this helps.
