I don't know what made us choose Jack.... both Andy and I wanted to name a son Jack, before we even met. I had a list of names I liked for future babies in my trinket box, since my teens, and Jack was at the top of it. Aidan was next on the list - at the time it was an unusual name - but we didn't go with Aidan as a middle name, it just didn't seem to flow with Jack. We decided that since I took Andy's family name when I married him, that Jack would have my maiden name as his middle name, and any future boys would also have a middle name form my side of the family.
That's how Angus got MacKenzie as his middle name. And Angus, well I just loved it - Andy did not, but I bought his approval with sexual favors

(might have to edit that out later)
Mia Isabella was an easy one, that was the tops on my girl list, so she was Mia Isabella as soon as the U/S confirmed she was a girl. To me it means my little beauty.
Sydney was a boy for a couple months, the first U/S was wrong, and she was going to be Vaughn. Then we found out she was a girl. First I wanted Caitriona, but he said that made him think of Hurricane Katrina. Then for a while I thought we had settled on Zoe Soleil, until he confessed he really didn't like that either. Finally it was the wek he was leaving for Iraq and time was running out to choose a name together so i got out my favorite baby name book and read every name, taking note of each one he didn't veto outright. Then I pared it down to the ones I really liked, and gave it back to him to choose. He had to leave before we settled on a middle name, but the day before she was born I just fet I wanted it to be Jolie, emailed him for his opinion, he liked it , and since I had her the next morning that was it.
So, no real fascinating meanings behind any of them, but I love them all.