Off in the rhubarb?? That's an amazing saying! Is that even a real thing or did you make it up?
Ava feels very faddish to me. Much more so than Emma. It feels like Emma has a much longer history and is used in many more languages than Ava, which has only become super-popular recently. For me, Ava is in a group with the -ayden boys and and -aylee girls. An explosive but passing trend.
Eva also has a long history and is used in many languages. Of the three (Eva, Ava, Emma) this would be my choice. Plus Eve and Evie are delightful.
Katharine versus Eva...Do I have to choose? I think they would make very nice sisters. Classic and timeless.
Genevieve Katharine is very very nice as well. Personally, GEnevieve is not really my style, but I can definitely see the appeal of Genevieve nickanme Eve/Evie. Some good options there!