WordPress MultiSite Question

Hey guys, quick question...

I have a client who has two websites, in one of them they sell online courses, and other material for homeschooling.

On the other sub domain, they want to actually host their online courses, like an academy.

They want to make everyone register in the naked domain, but have access to the online courses in the sub domain. Is this possible via wordpress multisite? or any other plugin, system, etc?

Any insight is welcomed. Thank you!