Summer Tana and Cordelia +ATK and -SPD.

Okay, if theyre both +atk-spd then you can do a few things.

Tana wants one of two weapons. She can keep her og weapon and fix that f-ed up speed, and then use it in a mixed emblem, or she can run a bladetome. Her A Skill should stay what it is, as it's strong and rare rn. Her B has to be desperation and her C is up to you. Special should be moonbow or glimmer IMO

Summer Cordelia however is actually kinda fine with her speed being a bit low. Not the best but she has blaringly fast speed to she works. I would recommend any speed boosting skills, akin to Fury, LnD, Swift Sparrow. Refine her weapon to be +spd or get a +spd slaying lance. I would keep her weapon however, as it adds another +2 to every stat (+5 to speed if you get the speed refine) on offense (+3 on defense) so it's not bad