ATP and Order fulfilment

Hi friends, we have the following scenario:

1. The customer places a sales order of 2 items to be delivered together from plant A

2. Only 1 item is in stock in plant A

3 Plant A needs to get the stock via an STO from plant B

4. Plant B also does not have stock and needs to do an STO on plant C

5. C sends to B and after GR, B sends to A

6. When A gets both the items in stock, it 'hard reserves' them for the customer

7. Both items being in A now, the delivery is done

8. We are open to bypassing B if it does not have stock and doing the STO directly from C to A if that is easier in SAP

We do have ATP running which needs to be considered i.e. the schedule lines need to be updated based on the process.

We are on ECC 6 EHP 8.

How can we achieve this plant search and auto STO creation process?

Happy to provide any more details.

Thanks!