Making a team with Nephenee

The best luck with team ive had for Neph was with Palla and Fae. Palla is well rounded for stats and can wall off both physical and magical green units pretty well overall, while Fae can sponge tank just about anything be it physical of magical. That trinity can do almost every single piece of content the game has offered so far, and i've been using them that way for 14 (thats a year + two months) and they very rarely let me down. The fourth unit is typically a healer, in which case veronica fits the bill nicely, while lately ive been using my pride and joy Maria for that honor.

Of those you showed, I would recommend Ryoma, as he has a nice well rounded stat build. A combination I've found exceptionally effective for him is Fury and the Brazen Atk/Res seal. His speed is high, his def is pretty good, but his atk needs a boost, and his res is quite low. Patching them up with the seal, and using Fury to help hit the HP threshold needed is a good way to start.

For your green, you're hardpressed to go wrong with Adrift Corrin. Dragons by and large are great at tanking and countering hard. If you want a more playerphase green, Bunny Sharena is a great choice, as she can also provide useful debuffs, as well as being able to take on the Blue tome units that would give Ryoma and Nephenee trouble.

Rounding out the team with Veronica is hard to beat. She is undoubtedly an OP staff unit in every way.

I run my Nephenee on a tactics team, perhaps you could emulate this team. I see you have a Bridal Sanaki and a Legendary Ike, if you were to promote a Titania you can build her like mine and make the rest of your units monsters. It would take a lot of Divine Dew but I can vouch that it would be well worth your time.