Hi ,
There are two aspects on your query -
Total Demand or Requirement = 7+2+2 = 11
Total Stock = 9
If you run MRP , then result will be Planned Order or PR of 2 based Net Required Calculation strategy = Available Stock including all recipient ( Based on MRP setup) - Demand Qty
MRP does not trigger any Availability Check ( ATP) during planning run !
Secondly , when Availability Check(ATP) is concern , it generally triggers on Production Order , Process Order , SO level to get the required stock and available situation ( Date ) so that system can allocate or propose the date of availability based on current stock availability , RLT etc .
Check the setting in OPJJ/ OPJK
Refer -Scope of the Availability Check - Material Requirements Planning (PP-MRP) - SAP Library
http://scn.sap.com/thread/3403439
Regards
JH