I think anyone hearing the set would first think ideas of magic, royalty, and European grandeur and only the name nerds’ll notice one doesn’t have an L.
But, ether way, I always think in deciding votes, you should favour the name on its own terms not as a sibset. This is because (and this is hard for a parent), your child is going to interact with the world primarily as an individual, not as a sibling. So I would pick the name you love the best over the perfect sibset name - assuming the name is broadly in sync and equitable, which Seraphina would be.
Another factor for me is nicknames. I love the nicknames for Seraphina - Sera, Saffie, Raphie, Phina etc, much more than Ellie or Winnie for Elowyn (as much as I like Elowyn). Way too many Ellie names right now (and I don’t like the sound Ellie). Do you prefer any of the nicknames?
If you can’t get past the L, here are some magical L name names with fab meanings:
Evangeline/Evangelina
Evelina
Solara
Paloma
Calista (meaning!)
Liliana
Sibella/ Sybella (a good cross between the two?)
Eloise (as above)
Louisa
Solène
Opaline
Helena (looks like Milena but different if go -ayna sound)
Delphine
Elodie (Lola, Edie, Odie)
Celestia / Celestine / Celestina
Elisabetta
Wildcard: Seraphiel
But I wouldn’t let the L thing defeat Seraphina, if she’s your fave!