We mainly just picked them because we liked them.
Oldest DD-- Uncommon first name, middle name very old fashioned (religious significance)
Middle DD-- Very uncommon. I have never met another person with middle DD's first name. Born on St. Patrick's day so we decided to do an uncommon (male) Irish middle name
Youngest DS-- Kind of had to be "different" based on the sister's names, but most "unique" boys names seemed either too feminine or hyper-masculine to us. We went with Silas, a completely "normal" biblical name, but not popular (more old fashioned). His middle name is DH's grandfather's name (all the men in his family have the same middle name).
Ironically, the one we gave the "normal" name to often gets his name mispronounced and I've even been asked twice if I made the name up.
We had some parameters which included not using my DH’s first name or middle name. His father was the reverse, so they just flipped the 2 names. No, just no. Also, didn’t want to have a “little Joe and big Joe” type thing.
All the women on my maternal side have their own names, but before this generation there were only three male names. Even my dad (married in) had one of the three names, and then they named my brother a "junior". My husband was the first non-George/Robert/John in the family and we made sure our kids had different names.
And we did not tell ANYONE our choice until kiddo was born - didn't want any input from other family members/friends.
We did the same. Partially because we wanted to see the child before deciding if a name suited them, but mainly because we didn't want input. It's pretty common for people to give strong opinions on theoretical names, but it would be pretty rude for them to comment on the name after it was already given.
Even just suggestions while we were still at the hospital and hadn't decided yet were annoying enough. (My siblings were lobbying hard for "Patricia" for DD's middle name) I couldn't imagine it being a constant discussion for months throughout the pregnancy.