Chars, Team, what you think? ^^

Not sure what are you looking for. Help with Arena? Help with stratum 10? I am going to say the team lacks synergy though the individual units do okay by themselves, except Effie, she kicks lots of ass standalone (just needs help moving around).

Do check the IVs, certain units don't give a shit (Effie), and some units are very sensitive to IVs that can make or break them. Would help to show all your units, maybe you have some sleeper 4*, 3* lying around.

Eirika-Nino-Ninian tandem is very fun if you keep nino buffed and the 3 of them work very well together (but not so separately). Nino can function well and kick ass at 4* if you don't have feathers to promote.

Based on what I see, I'll split your units into categories

Good as they are : Effie, Merric, Julia, Eirika, Ninian, Nino, Karel, Kagero, Ytiki

They do not need alot of skill inheritance to perform at their roles, but skill inheritance makes good units fantastic units. That being said, Merric simply goes from being good to very good (not quite fantastic) because he has competition with Julia and Nino for green tome position. Both Julia and Nino trump him in damage output easily, while he...is tankier than both and can shoot fliers. Karel goes from good to very good, but faces alot of competition for red slot. He starts murdering shit when he hits below 50% hp, but good luck keeping him there. Ytiki needs only minor tweaks to be a cute terror in battle.

Kagero is a unique infantry slayer. And 70% of popular units are infantry. you do the math.

Good units pre-inheritance who lose to better stat-bags : Catria - her default skill set is decent and she requires little modifications, but cordelia and hinoka both come with better offensive stats and brave lance+.

Requires serious modifications and supports to excel : Leo, Roy, Seliph, Lilina, Fae, Nowi, michalis/beruka.

Leo needs horse emblem buffs and Tharja's blade tome to become one-shot terror on a horse, without it, he's verging on trash tier. Roy is very balanced, but it means he lacks any particularly outstanding role. Jack-of-all-traits, but can be modded to be better in whichever role you need him to fulfill. Seliph needs alot of work to go from trash tier to okay. I have yet to see anyone make Seliph really good, and he's like a free win for me in arena. Lilina is like Julia stat-wise but she needs a better tome and skills. Fae really could do with lightning breath+ and someone to get the falchions away from her. Unlike poor Fae, blue Nowi can take swordbreaker or triangle adept to snap the falchions in half.

Michalis and beruka are very similiar, beruka is slightly tankier, but loses alot of offense power. Both are low res slowpokes that get shredded by mages, even blue ones. Requires significant changes to their existing skillsets but they can do very nasty damage if you mod their skillsets to favour that massive def stat. Both do okay if modded, gets crazy with flier emblem support. I did reply to a thread on how to build "flying tank" if either one interests you.

Skill inheritance Fodder : Hawkeye, Rebecca, Florina

hawkeye has deathblow, Rebecca & Florina have darting blow and good assist skill. Sorry just trash tier.

 

I'd be listing units that you may consider training, as well as desirable IVs.

1. Reinhardt - preferably +Atk. -atk flat out sucks for him. He doesnt care abt -spd.
2. Chrom - preferably +atk. +spd helps decrease the no. of units that can double against him.
3. Ogma - Preferably +atk. +spd means you can make a fast brave user who may hit x4. -atk sucks ass.
4. RobinM - preferably +atk, +spd or +def. -atk, -spd are both very damaging.
5. CorrinM - preferably +spd. Give him darting blow, I suspect it stacks with Yato's +4 spd. Vrooom vrooom.
6. Nino - preferably +spd. +atk also can work. If she gets -spd, it really sucks. -atk can be overcome with blade tome.

Good Skill Fodders at 4 stars

1. Hinata - Fury 3
2. Henry - Ignis and Gtomebreaker
3. Fir - 4* Glacies
4. Matthew - Hone speed
5. Florina - darting blow
6. Niles - Iceberg
7. Saizo - poison strike
8. Sophia - fortify res

 

Reinhardt - not best, but viable (your 2nd choice if you don't like RobinM)
Chrom - its okay to be neutral
Ogma - thats it, he's brave sword+ fodder
RobinM +spd/-def (pick this one, its a decent IV)
CorrinM - this is good IV
Nino +res/-hp (this is somewhat neutral, viable IV) - 3rd choice

I'm using -hp+res Nino as well, because no better IVs.

Eirika - that's it she is rally/hone/buff bot
Karel - not best, but viable. that's 50hp you are looking at.
Ninian - one of her best IVs. keep using her.
Kagero - this Kagero, put on hold

 

Yes, the team that QuickBit suggested works. I mentioned before, that some units can be viable even without the best natures. +spd helps avoid getting doubled by other units, so you could say speed works as both an offensive and defensive stat.