How to allow the user to choose from a pricing package yet be compatible with volume purchase and family sharing
You are correct that there are challenges with subscriptions and I would set aside VPP for now and focus on the tiers. Too many options will confuse everyone and complicate your efforts to track.

The Omni group does excellent work here - they offer a free app with read only functionality and a free trial subscription and two tiers. You could emulate their Mac App Store model quite immediately for either full purchase (and then annually release a new version)


https://support.omnigroup.com/omni-store-or-mas/


I would then look at VPP - you can push your app to specific clients at pricing points you agree upon, or let them know you'll refund / rebate / discount them post purchase if it's too much work to negotiate one off SKU in the B2B / VPP store.

The benefit of this approach is you still get your free/basic/pro functions through IAP and can toggle the family share feature with one build and one review. You can even roll in a discount for IAP based on previous purchases - so everything I can see you need has already been done (and works for years already).