Does falling star is 2 instance?

Yes — Falling Star deals its damage in two separate instances of 3 damage.

The spell reads "Deal 3 to a unit. Deal 3 to a unit. (You can choose different units.)," so each "Deal 3" is its own damage instance. You can split them between two units or stack both on one (6 total). The spell resolves as a single chain item, so nobody gets a reaction window between the two instances — your only chance to respond is before Falling Star resolves (FAQ #8639). Note that effects like Deflect get paid per instance that chooses the unit, so targeting the same Deflect unit twice means paying that cost twice.