Why didn’t you choose “Beyond [name]Emma[/name] and [name]Ethan[/name]” or “Beyond [name]Emily[/name] and [name]Ethan[/name]”?
The only reason why I’m wondering is because they’re more popular than [name]Ava[/name] and [name]Aiden[/name].
Obviously I don’t know for certain, but I think it may be because the names sound better together, probably because of the repeating ‘ay’ sound (rather than eh-ma/eh-mily and ee-than). I could be completely off the mark, of course!
I’m thinking that [name]Pam[/name] and [name]Linda[/name] chose [name]Ava[/name] and [name]Aiden[/name] instead of [name]Ethan[/name] and [name]Emily[/name], because unlike [name]Ethan[/name] and [name]Emily[/name], two standard classics that have been popular for a long, long time, [name]Ava[/name] and [name]Aiden[/name] became extremely popular/trendy out of the blue, and their epidemic popularity is specifically associated with the first decade of the 2000’s.
Likewise, they chose to name one of their older books “Beyond [name]Jennifer[/name] and [name]Jason[/name],” because those names were the most overused names that were most identifiable with the specific time period around which they wrote the book.
While an [name]Ethan[/name] or [name]Emily[/name] may have been born anytime, when I hear [name]Ava[/name] and [name]Aiden[/name], I think of overused names with a trendy feel from the late 1990’s/first decade of the 2000’s. To me, [name]Ava[/name] and [name]Aiden[/name] are today’s version of the 80’s [name]Jennifer[/name] and [name]Jason[/name]. [name]Just[/name] as I assume that a [name]Jennifer[/name] of today was born in the 80’s (or latter half of the 70’s), 10 years from now, I think that [name]Ava[/name] and [name]Aiden[/name] will forever be connected to the first decade of the 2000’s.
Granted, this is just a guess, but it’s the first thing that entered my mind when I learned of their book’s title.
[name]Jill[/name]–As always, you really hit the nail on the head. [name]Ava[/name] & [name]Aiden[/name] seemed time-specific (we even used the untraditional spelling of [name]Aidan[/name]/[name]Aiden[/name] (with some misgivings) because it is more popular today.) One of our previous subtitles for a [name]Jennifer[/name] & [name]Jason[/name] update was [name]Madison[/name] & [name]Montana[/name]–[name]Madison[/name] because it was THE trendy name at that moment, [name]Montana[/name] as representing a whole genre of 90s western place names–[name]Sierra[/name], [name]Dakota[/name], etc.
Thanks [name]Linda[/name]! 
I wonder what you next “Beyond…” book will be titled!