Minecraft on Xbox 360 & Xbox One?

Sorry it won't an Xbox one is more powerful than a Xbox 360. Xbox one can do more and the worlds can be bigger. It'd be very hard for Microsoft to do it cross platform on different gen consoles. Sorry again but you can't.

Not yet, though that will change later this year with the "Better Together" upgrade that is supposed to allow all players (except those on Sony platforms) to play on the same worlds online.