5th dnd – Part hidden before the attack. Surprise? Advantage? Both?

Our clever heroes found the goblins in a small encampment in the woods. Completely unaware of the threat that surrounds them, the goblins are sitting around a fire, easily prey to the band of hidden adventurers hiding in the trees.

The party is attacking! Arrows rain, spells are thrown and sword bearers rush into them. Our group …

Attacks to the advantage because they are hidden?
Gets only a surprise trick to catch the goblins without knowing it?
Both have the surprise and the advantage?

What are the scenarios in which each of the above would happen?