Skill Sets for Leo, Ares and Summer Elise

I'm not sure what vel is - I'm going to assume it's def for the time being. For Leo, I'm a big fan of Raurblade+ and Close Counter. He has good mixed bulk, and with access to cavalry buffs, Raurblade can do a good job at patching up his mediocre Atk. His refined Brynnhildr gives him a good niche but it costs a lot of Divine Dew and +HP/-RES is probably not a great IV set for that build.

For Ares I would just recommend adding Vantage and maybe Savage Blow to his base kit. Vantage has good synergy with Dark Mys and Brazen, and it helps slightly mitigate that -Def bane since hopefully he can KO with Vantage before taking too many hits.

Summer Elise does well with Bladetome, especially since her IV's don't touch her offensive stats. You could give her a tactic skill and run her on mixed teams and tactic buffs, or just run her with a buff bot like Eirika or Ephraim