Tom Cowles, 21, and his brother Ben, 20, wore hooded tops as they appeared before magistrates in Norwich.
The pair were members of the Norwich Lads Amateur Boxing Club and represented Norfolk in national championships when they were aged 12 and 13.
Millionaire Mr McGarahan, 45, of Much Hadam, Herts, suffered fatal injuries when he was allegedly kicked and punched in the early hours of Sunday.
The Barclays executive had been for a quiet drink with brother Kevin and cousin Sean Ryan and is said to have been set upon after going to the aid of Lithuanian Robertas Sinkevicius, 35, who was allegedly attacked while queueing at a taxi rank.
The Cowles brothers, from Costessey, Norwich, each spoke only to confirm their name and address during the brief hearing.
Ben Cowles is also charged with three counts of assault occasioning actual bodily harm to Mr Sinkevicius, Mr Ryan and Kevin McGarahan.
Solicitor Simon Nicholls, representing the brothers, did not ask for bail but said an application would be made in the future.
The brothers, who did not enter a plea, were remanded in custody to appear at Norwich Crown Court on October 17.
Their mother Joanne sobbed in the public gallery as they were remanded.
Afterwards Mr Nicholls said: “Both continue to maintain their innocence. Both voluntarily went to police to help with inquiries.”