Sharing INREACH with Family Members

It does seem like you have to share the account together with the device. It is a bit limiting, I agree.

This feature is only available with "professional accounts" (or whatever they call it this week).

If you have the optional "SAR insurance" (which isn't really insurance) from GEOS (or whatever they call it this week), you should be aware that this covers ONLY the subscriber. It does not cover family members using the device. This is not typically an issue in the US (where SAR typically does not involve out of pocket costs), but can be an issue elsewhere. YMMV, even in the US. 

You can share the device (linked to your accout) with your son. SOS feature is available for any user of the device, not necessary device/account owner. But you'll need to update the emergency contacts/preset messages manually, there are no user profiles (on non-professional subscription). I think you can keep your info (name, e-mail etc.) in the My Info section, just add your son details into the Emergency Notes and your contact details into the emergency contacts. And update the preset messages to include your phone number.

Once more. Yes, SOS will work. BUT if you subscribe to the supplementary "insurance" from GEOS, ONLY the actual device owner is covered by the "insurance".

Thanks for the helpful comments and assistance, much appreciated.