Can someone help me build a team?

Man, you got some good Swords.
To be quick:
Ayra or Mia, as they're busted and you seem to have Ayra supported. Those two can play a physical offensive role well enough with their base sets. Might wanna have a buff skill on her C-slot, to help out...
Taitiu, a powerful Blademage that'll probably destroy everything when given a buff. You'll probably wanna rank her up so that she can damage enemies more effectively.
Next is Ninian, for obvious reasons: she's a dancer. She'll let nukers like Tailtiu do their jobs.
You kinda don't have too many amazing greens or crazy good tanks, but Cherche can probably round out the team well enough. Either invest in her defense and give her fury and a defense refine, or go all in with death blow brave axe.

Congrats on so many good units!!! I don't have mia or arya.....

Arya/Ninian/deirde/Ike

I'm guessing your new but played the game for a while(based on the number of 5* you have)
Well I recommend to have of team that consists of "Tank"(either physical or Magical or better both)"Magic nuke"(Blade tomes)Physical nuke(units that can kill almost every unit in the game) and a Class killer(units that have weapon that are specifically for a certain unit. If you struggle against horse unit then have a unit equip horse killer weapons if dragons have a Flachion user or Naga)

Here are my team compositions:
1: Joshua
Nino
Ayra
and Deiredre

2.L!Ike
Fjorm
Ayra
Nino

3.Mia
Deirdre
Felicia
Fjorm
(this suggestions are not the best team composition)

For me I just put random Unit that I think can work and Make them work though it takes some getting used to the team and make tactical plans.

Just avoid using Merric and I think you'll be able to find a team composition that fits your play style in due time. You have some real good reds (Ayra and Mia especially), and you should probably consider using that Ninian of yours for dancer utility. It'll come in handy at one point or another. Just make sure that you've covered all of your bases (weapon type, color, magic attackers, etc.) in your team and don't go with all reds, no matter how good yours are.