If you want clients to be automatically added to a specific group on install, then just tick the "Add clients automatically to the selected group" checkbox when creating the client install package, and select the group.
The MSL's you're looking at can be embedded in the client install package, but have no influence over which group the client appears in.
And just to reiterate one last time, no matter where you install the client, all the SEPMs will know about them and display them if you're replicating.
At this point, I'd highly recommend you enrol on the online training offered by Symantec, or perhaps reach out to a Symantec Partner who can set this up for you, as providing very specfic instructions via the forums may not be the most efficient or effective way of getting to know the product.
More on Symantec's online courses can be found below:
https://www.symantec.com/content/elibrary/selibrary.html