I trust you do realize that those are two separate questions. Whether you fly on AA or BA, you can choose to credit particular flights to either program -- or to any other oneworld FFP.

If you fly AA between MAF and DUB, you have the option of a single connection, and get to pre-clear U.S. Immigration and Customs at DUB on your trips home. Flying BA would entail a minimum of two connections, and no use of U.S. preclearance facilities. In addition, as long as you are at least AAdvantage Platinum -- not even Platinum Pro -- you could select MCE seats at time of booking on an Economy ticket; but that's irrelevant if you would only be flying PE or Business.

Your oneworld Sapphire or Emerald status would also entitle you to free seat selection at time of booking if and when you chose to fly BA. As long as you can comfortably maintain at least AAdvantage Platinum status, I would probably stick with crediting my flights to AA.

As for your son, I think a lot depends on whether he is likely to do much -- if any -- intra-European flying when in DUB. If yes, having a stash of BA Avios might serve him well for those flights.

Also remember that when you redeem BA Avios for trans-Atlantic travel on either AA or BA, you will be hit with hefty carrier surcharges. When redeeming AAdvantage miles for trans-Atlantic travel, you will be hit with hefty surcharges when flying BA, but none when flying AA. And when redeeming AA miles for award travel, connections are included in the redemption rate. By contrast, BA charges extra Avios for each additional leg flown.