If multiple players have immunity and play idols at tribal council here's what will happen:

If all votes are voided and multiple players are vulnerable (didn't play idols or have immunity) a revote will occur.

If all votes are voided and one player is vulnerable (didn't play an idol or have immunity) that player is sent home by default as they are the only person who can voted/rocked out in a revote or tiebreaker.

If all votes are voided and nobody is vulnerable then the player who has immunity is the only person who's safe and the players who played idols will be forced to draw rocks.

If final tribal council ends in a tie.
Then any jurors who did not vote for the tied players will revote.
If every jury member voted for a player involved in a tie then an additional juror will break the tie. The additional juror will be the next player closest to making the jury.