The Cricket Regulator - a body independent of the England and Wales Cricket Board (ECB) responsible for enforcing regulations - on Wednesday issued cautions to Brook and Bethell for breaching player conduct rules.
Brook claimed originally that he was on his own when he got involved in an altercation with a bouncer at a Wellington nightclub on the eve of a one-day international on November 1st, an incident that was only revealed two months later.
Brook was fined £30,000 by the ECB and given a final warning.
He later admitted that Bethell and fast bowler Josh Tongue had been present, explaining he had lied to try to protect his team-mates and publicly apologised.
Brook and Bethell both played in the match the next day, which England lost by two wickets to complete a 3-0 series defeat.
No action was taken against Tongue, who was not in the one-day international squad at the time.
The Regulator "issued a caution notice to Harry Brook and Jacob Bethell in relation to their conduct", said a statement.
It added that both players had accepted they were in breach of the professional conduct regulations.
Many observers believed Brook was lucky to retain the captaincy for the T20 World Cup, where he led England to the semi-finals before losing to India in Mumbai.
England's off-field behaviour in Australia before and during the 4-1 Ashes defeat came under heavy fire, with allegations of poor preparations, muddled team selection and a "drinking culture".
England players were photographed spending hours in bars during a mid-series beach resort break, with a video of an apparently drunk Ben Duckett circulating on social media.
England Test captain Ben Stokes, coach Brendon McCullum and director of men's cricket Rob Key all kept their jobs after an ECB review of the tour.