hi fazila ,
Thank you for moving your questions here.
The explanation is great - now it makes more sense. Not very good news though as the only way you can track at product level with multiple SKU would be using the Multi Inventory add-on. Problem is the front end ordering and splitting these inventories according to user roles.
We are planning to work with or on a membership plugin later in 2021, but we have not decided what plugin that would be. So for now, I am not sure we can help?
Thinking about it, you could achieve what you want with Product Levels add-on! But only after we release the next update.