Magnolia Jane is darling. Adelaide is beautiful with Magnolia. Love Margot too. Jethro would fit with Margot or Oscar as siblings. Oscar fits with any of the girl names imo.
With Magnolia Jane in mind as your top girl name, I’d suggest:
Camilla
Evangeline
Guinevere
Susannah
Alice
Calla
Georgiana
Elsie / Eloise
Florence
Verity
Clara
Hazel
Estelle / Stella / Estella
Tessa
Cosette
Hattie
Mabel
In line with Jethro / Oscar, I’d suggest:
Ellis / Elliott
Hugo
Finnian
Reuben
Vaughn
Tobias
Cyrus
Desmond
Cormac
Benji
Wallace
Clarke
Langston
Phineas
Callum / Calvin / Callahan
Graham
Winston
Donovan
Samson