Louisa - it's ok. Not one I'd choose but elegant and pretty Agnes - don't particularly like it, it's too old lady for me. Rosamund - it's ok. Prefer the other Rose based named Miriam - really like it Kezia - like it Jennifer - like it but don't like Jenny which seems inevitable Katharine - like it but this is a very unusual spelling? Dislike Kathy Vivien - don't like it at all but for some reason do like Vivienne?! Joanna - love it Wilhelmina - gosh no, really really dislike this. It sounds so ugly. Caroline - not keen. Susanna - like it Martha - like it Julia - it's ok but don't especially like it. Love Juliet though. Mirabelle - very fancy but quite like it.
I'd choose Joanna followed by Miriam.
I do think Paul is a bit too dated but then a lot of your girl list is from a similar time.
I wouldn't worry about dated to be honest. Paul is a classic name with plenty of history, I don't think anyone is going to laugh at him for having an "old-fashioned" name in the same way that they might if he was Albert or Ernest. (or have those come back now?)
There are no names on your girls' list I really don't like, but I think the nicest of all are Rosamund, Joanna and Julia. If you might still want to use Paul at a later date if you have a girl, Joanna and Julia would probably go better with it, as Rosamund is a bit "romantic" whereas the others are more down to earth.
I love Louisa, Keziah, Susannah, Mirabelle. Pretty and underused. I like Miriam and Caroline in theory but cant imagine actually using them! Agnes and Wilhelmina are ugly Jennifer, Katharine, Vivien, Joanna are all OK but a bit dull Martha is nice Julia is a bit dated but I love Juliet
Louisa - lovely, classic, elegant and understated Agnes - grumpy and old womany Rosamund - prefer Rosanna Miriam - busybody Kezia - prefer Keziah Jennifer - quite 70s Katharine - prefer Katherine, lovely classic name, nn Kate or Kitty Vivien - prefer Vivienne Joanna - 70s Wilhelmina - Enid Blyton! Caroline - due a come back Susanna - lovely an graceful Martha - over done at the moment Julia - like the full name, don't like Juju, Julie or other nn I have come across Mirabelle - lovely, really pretty