Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.601 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
"between AA and the credit card programs that transfer to one world airlines, you have no problem getting two tickets on one world airline (AA is one world) because you can redeem one ticket from one program and one ticket from another program"
Two problems with that:
1) Partner miles can only be redeemed for AA SAAver seats, which the OP seems to have trouble finding.
2) Redeeming BA Avios for TATL flights on AA, BA, or IB will incur hefty surcharges.