marc wabafiyebazu , 15 , plans to plead not guilty if charged with felony in connection to monday 's deadly shooting .
wabafiyebazu 's 17-year-old brother , jean , was shot dead , along with 17-year-old suspected drug dealer joshua wright .
wabafiyebazu brothers reportedly tried to rob a group of miami drug dealers .
their mother is roxanne dubé , the recently appointed canadian consul general in miami .
the boys had driven to a house with a third friend to reportedly purchase two pounds of marijuana for $ 5,000 .
gunfire erupted soon after they entered , though marc was in the car at the time .
anthony rodriguez , 19 , who was wounded , was also arrested on charges of felony murder .