Opening statements will be delivered Monday for what is expected to be a 10-day trial.
The Morris brothers were indicted by an Arizona grand jury in 2015. They are accused of helping three other people beat 36-year-old Erik Hood outside a Phoenix recreation center.
Two of the other co-defendants pleaded guilty Wednesday to aggravated assault charges.
Police say Hood was leaving a high school basketball game when he was approached by a friend of the Morris brothers. Hood told Phoenix police the man was speaking to him when he was punched in the back of the head.
Hood ran to his car but fell down before five men, including the Morris twins, punched and kicked him repeatedly, authorities say. All five left in a Rolls Royce Phantom.
Hood told police he sustained a fractured nose, abrasions and a large bump on his head.
Police say it is alleged that Hood was assaulted for sending an inappropriate text message to the Morris brothers' mother.
Hood is an acquaintance of the Morris brothers and reportedly had a falling-out with them in 2010.
The NBA players could face a maximum of nearly four years in prison if they are found guilty.
The 6-foot-9 twins became teammates in 2013 when Marcus was traded to the Suns.
Both were later traded to other teams.