[name_f]Sylvie[/name_f] [name_f]Maren[/name_f] is so beautiful and sweet. I love that it has meaning for you, too.
I also think that [name_f]Sylvie[/name_f] fits in perfectly with big brothers E & W!
(also, I think that [name_f]Sylvie[/name_f] can definitely work as a full first name. I’ve met a couple, and I’ve never thought twice about it. I dont see it as too childish/unprofessional/etc! I think its lovely, and I actually prefer it to [name_f]Sylvia[/name_f])
[name_f]Sylvie[/name_f] is a beautiful name. I’m always puzzled why some people automatically think it’s a nickname for [name_f]Sylvia[/name_f]. It’s simply the [name_m]French[/name_m] form of [name_f]Sylvia[/name_f]. I guess many English speakers tend to think any -ie name is nickname but this is not the case with MANY [name_m]French[/name_m] names.
Anyway, I think [name_f]Sylvie[/name_f] is a beautiful name! [name_f]Sylvie[/name_f] [name_f]Maren[/name_f] is nice and I like it for you - it fits right in w/ the other names on your list (and your boys’)! I would personally would prefer something like [name_f]Sylvie[/name_f] [name_f]Marina[/name_f], [name_f]Sylvie[/name_f] [name_u]Marion[/name_u], or [name_f]Sylvie[/name_f] [name_f]Marianne[/name_f]. There is nothing wrong with the combo - it’s just matter of personal taste!
Good luck! 
I guess I just dont get everyone’s obsession with [name_f]Sylvie[/name_f] over [name_f]Sylvia[/name_f], but… yeah, I like the name, with [name_f]Maren[/name_f]. It goes with your sons names.
Consider [name_f]Sylvia[/name_f] [name_f]Maren[/name_f], though. You could use [name_f]Sylvie[/name_f] as a nickname and it wouldn’t even change nothing but make some random idiot on the internet happy.
[name_f]Sylvie[/name_f] isn’t a nickname, people!! It’s the [name_m]French[/name_m] form of [name_f]Sylvia[/name_f]. Goodness.
[name_f]Sylvie[/name_f] [name_f]Maren[/name_f] is lovely!
Thanks! That’s what we were thinking too. Especially with how popular names like [name_f]Sadie[/name_f], [name_f]Sophie[/name_f], [name_f]Mia[/name_f], etc are.