If opponent play a card and i react with a card that play Brynhir. when the chain resolve does opponent card effect resolve?

Yes — the opponent's card still resolves. Brynhir only stops new plays; anything already on the chain finishes resolving regardless of her.

One detail on sequencing: Brynhir's "When you play me" trigger goes on the chain above the opponent's card, so it resolves first and locks them out of playing anything further that turn — but their original card then resolves normally. They also get a chance to respond while her trigger is on the chain, before it applies (FAQ 3849).