IR/ISO between two sub-inventories

Give us some light on how to map the below requirement (Setups and process).

We have two different operating units.

X-OU, X-Inventory Org, X1, X2 are Sub-Inventory.

Y-OU, Y-Inventory Org, Y1, Y2 are Sub-Inventory.

The Sales Order will be booked in X-OU for the customer 'A' with the shipping warehouse as 'Y'.

Here the 'Y2' Sub-Inv is maintained by 3rd party, So, the IR/ISO will be created Y-OU to transfer the material between Y1 to Y2.

Once the material is transferred to 'Y2' sub-inv, the 3rd Party will send a confirmation file to 'X-OU' to receive the logical qty into there X2 sub-inventory.