User blog comment:IamJakuhoRaikoben/Chapter 358: Magical Barrier Particles, Review./@comment-24112129-20131101024945/@comment-7418318-20131101165850

Maybe Skiadrum and Weisslogia weren't able to teach them as well as Metallicana and Igneel, because of their age and sickness respectively.

No idea about Grandeeney though. I guess Wendy just took too long to learn the healing and support magic as a child for there to be any time left for combat training before the 7.7.X777 came.