Margot is beautiful. I actually really like Ursula but I'd be worried about what the shortened versions would be....although tbh you can fix that pretty easily by correcting people and thinking up a short version that you like yourself and sticking to it. (Arsey Ursey.....? Although Percy could at a stretch be a super cool girls shortening!)
On the Imogen theme, what about: Ishbel Imelda (I LOVE Imelda but hardly anyone agrees with me, I think it's strong and old and beautiful).
Esther I really like.
Reuben is so, so popular now. I know at least four all in different parts of the country and all with different 'types' of parent (hippy, academic, wee bit chavvy...), so I think it's a generally super popular name rather than just a name 'type' IYKWIM.
Easy to spell and the first suggestion is Siobhan?
Georgie (Georgina) I prefer Georgiana Jemima (DH not keen) I think puddle duck, what about just Jem? Alice I prefer Alicia and isn't this very popular atm? Nancy (don't like the Cameron connection) I don't think most people will think of the Cameron connection. He'll be forgotten soon anyway. Maeve I find this difficult to pronounce and quite old lady Una it's not very pretty Tess (possibly from Esther, possibly just Tess) too religious for me & working girl Ursula (how do you pronounce that middle syllable?!) Ur-sue-la phoebe's not very nice sister in friends
Isis Oralie Mabel Viola Vivien Rosabella Rosemary Roisin Rowena Rosabeth Hazel Heather Carol Carolyn Lucille Sylvie Joan Johannah Cerys