I remember reading and really enjoying a series of books aimed at approx 7-12 year olds - this would have been in the early 2000s. They were about a mixed friendship group (set in America I believe) who were able to shape shift, possibly after being struck by lightening. In one of the books, I think I remember one of them turning into Arnold Schwarzenegger...
I think they always had a kind of 'saving the day' theme, and also had to keep their power a secret from everybody else. I think they referred to themselves as 'morphs' too.
If anyone could help identify these books....! It has bugged me for years!