Kaytie was a character she made up herself. MishMash is the adopted daughter of Fury and fights for S.H.I.E.L.D. although she is not an Avenger per se. Her real name is Claire and she refuses to kill bad guys, she only defends the innocent, because she is a Christian superhero. Kaytie writes stories about her in her free time. Kaytie also designed and created her own costume.
Nate was also a character he made up himself. Maestro isn't as well defined as MishMash, but his superpower has something to do with magic and Nate designed this costume himself.
Daniel was Hawkeye. He made his own arrows out of dowel rods. I don't know what all went down in the garage during the creation of the arrows because I resolutely stayed away, but it did involve at least one cut finger and the demise of Daddy's favorite dowel rod. But that was all between them. :D
Abbie was Captain America. Of course. Nothing further needs to be said.