If all else Fails do as I do, at the airport ask an agent if you are sitting between 2 people with the same last name .If yes you are good to go as most likely they are together and will offer to switch seats with you so that you wont be keeping them apart.

If you are told No, ask if they can switch your seat to 1 where you are sitting between 2 people with the same last name, as long as those people dont have a higher status then you and the agent has some free time, it works or at least it has for me. I did explain my craz(y) reasoning and they usually said 'pretty smart'.