Take or leave of course but I don’t think I’d choose a coastal word name when the surname is already [name_f]Summers[/name_f] - it feels a little too thematic for me. [name_f]Coralie[/name_f] [name_f]Winslet[/name_f] [name_f]Summers[/name_f], for eg, feels quite nature-inspired/topographical all together (with each name being on that theme), whereas [name_f]Charlotte[/name_f] [name_f]Beatrice[/name_f] feels much more classic and traditional. I don’t see them as natural sissies! Maybe [name_f]Coralie[/name_f] & [name_f]Ida[/name_f].
If you’re set on [name_f]Charlotte[/name_f], I think I’d lean towards two classic names for her sister, too, for that same timeless, old-money feel. [name_f]Penelope[/name_f] [name_f]Mary[/name_f] [name_f]Summers[/name_f] would be lovely, or something like [name_f]Helen[/name_f] (maybe nn Leni), [name_f]Caroline[/name_f], [name_f]Frances[/name_f], [name_f]Georgina[/name_f], or [name_f]Annabel[/name_f] (maybe nn Nan). To me, coastal old money is more understated and vintage than overtly beachy, if that makes sense! So don’t add to [name_f]Summer[/name_f] imo.
Of the options listed, I’d probably go for [name_f]Mary[/name_f] [name_f]Eloise[/name_f] or [name_f]Mary[/name_f] [name_f]Isabel[/name_f], as they feel the most in keeping with [name_f]Charlotte[/name_f] [name_f]Beatrice[/name_f]. I do like [name_f]Marloe[/name_f] and [name_f]Maris[/name_f] as nicknames too!