To expand on what others have said, be aware that the game of Magic has its own glossary of words. 'To cast from your hand' has a very specific definition, involving many steps, like picking the a card in your hand, placing it on the Stack and paying its cost, to name but a few. This is much more complex than the simple displacement of cards.

Beacon of Unrest is a spell. When it resolves, all it asks you to do is to displace two cards:
-displace one card from the Graveyard to the Battlefield (Dread Cacodemon)
-displace one card from the Stack to the Library (Beacon of Unrest itself)
And that's it! The only card you actually cast is Beacon of Unrest; the Demon card simply gets displaced, therefore its ability never fires off.

The triggered ability on either of those creatures won't trigger since the condition isn't met, but Beacon of Unrest will still put the creature onto the battlefield. Strategy-wise, if you're building a deck with Beacon, you should find a different creature to reanimate.

You're right, neither of those triggered abilities will trigger because you didn't cast the demon from your hand.


You still have a big demon on the battlefield, you just don't get their mass destruction effect.