Hi Rahul,
For message split you can use the multi mapping concept: Developing Multi-Mappings for Message Splits - Enterprise Services Repository - SAP Library
You have to take into account that your scenario must be asynchronous to use multimapping, nad you will need to split the message at mapping level with the different line items. Check an example of multimapping http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/90dcc6f4-0829-2d10-b0b2-c892473f1571?overridelayout=t…
From my own experience you can work in this order:
1. Do the ESR mapping, loading the XSDs or WSDLs and to work until you can do the right split. It should be a bit complicate with your first split.
2. Work with the multi mapping concept, and to check that you are generating two messages correctly.
3. Talk with the endpoint developers if they can provide you a way to know if the messages are coming and doing their stuff correctly.
Regards.