How to have same items in 2 different company associated with same Facility?

Summary:

We have Facility: DC01 sharing with Company: Co1 & Co2. Co2 is treated as an internal company and we do inventory transfers from Co1 to Co2. But to reduce the user count in the instance we have created all the users in the Parent company PC. Also, as it belongs to the same Facility the users are the same as those who do the transaction in Both companies.

But we are facing an item code ambiguity issue, because the item master is ame for both companies.

How to overcome this?

We don't want to have 2 accounts for the same user in Co1 & Co2.