As each temple is a different object, and their abilities do not stack, you would have to first complete the ability of one temple before going on to the next one.
A.) Yes.
B.) There is no test stating that if you used another temple you must do the same thing for the second one. As I said each temple is a different object and, unless there is some text stating otherwise, each should be treated completely separately. They do, after all, each have their own ready marker, and you don't have to use both at once. You could save one for a different attack if you wanted.
If your friend is correct, then on the next attack you would have to do the same thing you chose for the first attack. But what if you chose to reroll the D12 on the first attack and the second didn't have an effect roll?
This game is supposed to be realistic, and I don't see how forcing a temple to do the same thing as the first one would be realistic.