[name_m]Hi[/name_m] there.
Here are my thoughts on your lists:
Boys-
[name_m]Gavin[/name_m] Joseph-This seems just about perfect w/Trenton. It’s simple & masculine & strong & sleek. Well known but not terribly popular.
[name_m]Colin[/name_m] Joseph-I love [name_m]Colin[/name_m]. I personally like it more than [name_m]Gavin[/name_m]. It’s similar, but a little softer in my opinion. [name_m]Gavin[/name_m] is a bit more popular, if that’s a concern of your’s.
[name_m]Ethan[/name_m] Joseph-This is very popular, & not my favorite. Not sure why. Maybe it’s just over done. It doesn’t feel as handsome as the others.
[name_u]Darren[/name_u] Joseph-I really like this for you. It’s manly but kind & smart. Simple but kind of unexpected, just like [name_m]Trenton[/name_m].
Sooo, I basically am no help! I like [name_m]Colin[/name_m] best myself, but I kind of am loving [name_u]Darren[/name_u] most as a little bro to [name_m]Trenton[/name_m].
Girls-
Elizabeth-I love [name_f]Elizabeth[/name_f]. I think that it’s quite nice w/Trenton, & has a lot of great nns if you’re into those. It’s such a smart feminine strong classic. I think that [name_f]Elizabeth[/name_f] [name_f]Josephine[/name_f] would be good. But maybe [name_f]Elizabeth[/name_f] [name_f]Clover[/name_f], [name_f]Elizabeth[/name_f] [name_f]Dahlia[/name_f], [name_f]Elizabeth[/name_f] [name_u]Juniper[/name_u], [name_f]Elizabeth[/name_f] [name_f]Marigold[/name_f] or [name_f]Elizabeth[/name_f] [name_f]Magnolia[/name_f]?
[name_f]Taryn[/name_f] Josephine-I’m not a fan. It does feel gender neutral to me, & also too cutesy w/Trenton.
Here are a few suggestions that you may like:
Boys-
[name_u]Austin[/name_u]
[name_u]Alden[/name_u]
Casey-okay, kind of gender neutral, but so cute on a boy!
[name_u]Holden[/name_u]
[name_m]Ivan[/name_m]
[name_m]Malcolm[/name_m]
[name_u]Wyatt[/name_u]
Girls-
[name_f]Audra[/name_f]
[name_f]Bridget[/name_f]
[name_f]Cora[/name_f]
[name_f]Gemma[/name_f]
[name_f]Gwyneth[/name_f]
[name_u]Haley[/name_u]
[name_f]Katherine[/name_f]
[name_f]Lydia[/name_f]
[name_f]Molly[/name_f]
[name_f]Phoebe[/name_f]
[name_u]Sloane[/name_u]
[name_f]Hope[/name_f] this helps.