For defense, use Telluria only.
For offense they both have different uses, and are both good heroes.
You would need an emulator for that.
Android emulators are common, and easy to install. The one I use is BlueStacks.
iOS emulators, on the other hand, are not so common. Perhaps someone who knows more about those emulators can help you find one.
Yes, it’s fine to play on an emulator, as long as you don’t use other 3rd party software that interferes with the game.