Brook was fined by the England and Wales Cricket Board for the incident in October and apologised to England supporters at the start of the current tour of Sri Lanka.
The 26-year-old also insisted he was out alone on the night in question but the Telegraph reported that Bethell and Tongue were fined for their involvement and are also being investigated by the Cricket Regulator.
Brook released a statement following Friday's victory in the first T20 in Sri Lanka, which read: "I accept responsibility for my actions in Wellington and acknowledge that others were present that evening.
"I regret my previous comments and my intention was to protect my teammates from being drawn into a situation that arose as a result of my own decisions.
"I have apologised and will continue to reflect on the matter. This has been a challenging period in my career, but one from which I am learning.
"I recognise that I have more to learn regarding the off-field responsibilities that come with leadership and captaincy. I remain committed to developing in this area and to improving both personally and professionally."
The Cricket Regulator is independent from the ECB and has the power to bring disrepute charges if it has enough evidence.
News of the incident broke after England's 4-1 Ashes defeat, where the team were forced to face accusations of a "drinking culture" and Brook was asked about it on arrival in Sri Lanka.
"I want to say sorry to my teammates, to all the fans that travel far and wide and spend a lot of money to watch us play cricket," he said at the time.
"We went out for a couple of drinks beforehand and then I took it upon myself to go out for a few more and I was on my own there."
The ECB is conducting a review of the winter, with one focus on "behaviour" and some steps have already been taken such as the introduction of a midnight curfew for the players while in the sub-continent.
