Yup - you’ll need to adjust the ‘instance’ counter, but that’s the approach. As long as you’re using regular SIP devices, you should be good to go. Note that ‘WebRTC’ is an outlier on this, so if you are using that, PJ-SIP may not be the best method and using your Ring Group approach will probably work better.
Personally, I’d not use WebRTC and go with the PJ-SIP solution, but I’m adverse to pain.