I absolutely love [name_u]Wren[/name_u] + [name_u]Fern[/name_u]!
I am really into the idea of you continuing the nature theme but also using four letters. [name_u]Wren[/name_u] + [name_u]Fern[/name_u] are just so cohesive and I would definitely want to continue that cohesion.
This makes [name_u]Reed[/name_u] most appealing from your boys list. Personally I just see [name_u]Reed[/name_u] on boys and I appreciate that you’ve listed him with the both but for me [name_u]Reed[/name_u] is all boy. Anyways I love [name_u]Reed[/name_u] [name_u]William[/name_u] so handsome! [name_u]Wren[/name_u], [name_u]Fern[/name_u] + [name_u]Reed[/name_u] are superb 
You’ve had lots of lovely suggestions so count any repeats as me being in agreement with the berries
4 letter options…
[name_u]Cove[/name_u] [name_u]William[/name_u]
[name_m]Clay[/name_m] [name_u]William[/name_u]
[name_m]Oslo[/name_m] [name_u]William[/name_u]
[name_u]Rome[/name_u] [name_u]William[/name_u]
[name_m]Moss[/name_m] [name_u]William[/name_u]
[name_m]Oaks[/name_m] [name_u]William[/name_u]
[name_u]Bear[/name_u] [name_u]William[/name_u]
[name_u]Skye[/name_u] [name_u]William[/name_u]
[name_u]Lake[/name_u] [name_u]William[/name_u]
[name_m]Ford[/name_m] [name_u]William[/name_u]
[name_u]Dune[/name_u] [name_u]William[/name_u]
[name_u]West[/name_u] [name_u]William[/name_u]
[name_u]Onyx[/name_u] [name_u]William[/name_u]
[name_m]Oslo[/name_m] + [name_u]Rome[/name_u] aren’t really nature names but I think they work wonders
If your wanting to break the four letter theme
[name_u]Rivers[/name_u] [name_u]William[/name_u]
[name_u]Parks[/name_u] [name_u]William[/name_u]
[name_u]Indigo[/name_u] [name_u]William[/name_u]
[name_u]Rowan[/name_u] [name_u]William[/name_u]
[name_u]Beacon[/name_u] [name_u]William[/name_u]
[name_u]Horizon[/name_u] [name_u]William[/name_u]
[name_u]Bayou[/name_u] [name_u]William[/name_u]
[name_u]Ocean[/name_u] [name_u]William[/name_u]
[name_u]Coast[/name_u] [name_u]William[/name_u]
[name_u]Briar[/name_u] [name_u]William[/name_u]
Looking at your girls I automatically gravitate towards [name_f]Meadow[/name_f]! I think [name_f]Meadow[/name_f] doesn’t feel as ‘cool girl’ as [name_u]Wren[/name_u] + [name_u]Fern[/name_u] but I genuinely love [name_f]Meadow[/name_f] I also like the nature feel of the name. I really want another nature name for you!
4 letter options…
[name_u]Sage[/name_u]
[name_u]Dove[/name_u]
[name_u]Lark[/name_u]
[name_f]Iris[/name_f]
[name_f]Rose[/name_f]
[name_u]Rain[/name_u]
[name_u]Lane[/name_u]
[name_f]Opal[/name_f]
[name_u]Snow[/name_u]
[name_u]Moon[/name_u]
[name_u]Blue[/name_u]
[name_u]Bird[/name_u]
[name_u]Isle[/name_u]
[name_u]Nova[/name_u]
[name_u]Echo[/name_u]
[name_u]Teal[/name_u]
From this list I love [name_u]Moon[/name_u] and [name_u]Lane[/name_u] with your kiddos
If your wanting to break the four letter theme
[name_u]Prairie[/name_u]
[name_f]Reverie[/name_f]
[name_u]Sparrow[/name_u]
[name_f]Azalea[/name_f]
[name_f]Linnea[/name_f]
[name_u]Juniper[/name_u]
[name_f]Apple[/name_f]
[name_u]Aspen[/name_u]
[name_u]Berry[/name_u]
[name_f]Bloom[/name_f]
Clove/Clover
[name_u]Cricket[/name_u]
[name_u]Hyacinth[/name_u]
[name_f]Jonquil[/name_f]
[name_u]Sorrel[/name_u]
[name_u]Larkspur[/name_u]
[name_f]Hope[/name_f] this helps