Congratulations!
My favourite of these three is [name_f]Annabel[/name_f]! I love [name_f]Sylvie[/name_f] too, and I’m not a huge fan of [name_f]Philippa[/name_f] (prefer just [name_f]Pippa[/name_f]) but all three work well with your other children! If you like having nickname options, then I think [name_f]Annabel[/name_f] or [name_f]Philippa[/name_f] are the better choices. [name_f]Annabel[/name_f] could be Annie/Anna/Belle/Bella/Nellie/Abbie etc and [name_f]Philippa[/name_f] could be Pippa/Phia/Pia/Poppy/Lily etc. [name_f]Sylvie[/name_f] could be [name_m]Silver[/name_m] or [name_f]Vee[/name_f] but it doesn’t have as many options as the other two, but it depends on whether you want just one nickname you like or whether you like having multiple options.
I love your middle name tradition! Some more ideas…
[name_f]Foxglove[/name_f]
[name_f]Lovejoy[/name_f]
[name_f]Skylark[/name_f]
[name_f]Meadowlark[/name_f]
[name_f]Bluebell[/name_f]
Songbird / [name_f]Birdsong[/name_f]
Moonflower
Seawillow
Everblossom
[name_f]Honeysuckle[/name_f]
Winterberry
[name_f]Faerydae[/name_f]