1. You can't hold a seat on another carrier. AA may show it, but it's not out of Cathay's inventory until Cathay specifically reserves it and it's paid for (with miles, currency or whatever).
2. I would get your ducks in a row with all 4 of you confirmed with e-tickets to cover all segments for all travelers, before tinkering with anything. As you are finding out, this is a ponderous process with a lot to go wrong.