To edit the contents of a group, double click the group to ‘enter’ the group, then click to select an element. You should not need to ungroup items just to edit them.
I'm unclear on what you're referring to by a movie, but if you mean to restrict certain sizes, say give something a max or min width/height, there's no built-in way to do this. However there are some ways to do this with code; please see this post:
If you're just looking to restrict a movie from going fullscreen, I don't think there's a way to do that, but you could at least hide the video controls via the video options in the element inspector.