How to migrate applications to other user account without downloading the applications again?
If your device is rooted, you might want to take a look at Multi-User App Share. This app permits the owner to "share" installed apps with other users (which shares the apps only, not their data), so they don't need to be installed again. According to the app description and comments, this even works for paid apps (at least partly -- this feature is not yet fully tested).

For the other part (without root), see the answer of Penguinolog.