Depends on the route you are flying. Remember that AA will not award points on any BA transatlantic flights and that include flights from London to South America!

Otherwise, you will be getting full points on AAdvantage.

I am sorry but I do not understand the second part of your question..about BA being your 2nd carrier? As long as you fly ANY of the 5 carriers out of the 7 OneWorld airlines, you will get the 100K .