I'd do the kid a favor and just name him Carver. Carden is just strange, and I have a pretty good knowledge of Celtic/English names. Connor and Carter are more common but still better than Carden. Maybe consider:
Craig ...or pretty much anything but Carden!
Aiven and Carden would be lovely together!
I have to say, Aiven is an awesome name :)
I like the others on your list too, but I think they're too familiar with Aiven. So yeah - I vote Carden.
I like the name Carden. I went to high school with a Carden and he was a great guy with lots of personality. It goes well with your last name and makes a good sib-set with your first son. If it were me I would go for it!
I've never come across Carden before, but I think it fits right in with the surname-turned-first-name trend of today. I think it pairs well with Aiven.