Fuad Awale, 25, of no fixed address, and Sharmake Abdulkadir, 22, were found guilty.
Warsame Shire Awale, a writer, singer, comedian and radio personality, worked as a satirist for Radio Kulmiye.
Sharmake Abdulkadir, 22, told jurors he saw Fuad Awale, 25, kill the teenagers.
Awale, Abdulkadir and Mr Harun, of Fishermead Boulevard in Milton Keynes, are all of Somali origin, along with the two victims.
Abdulkadir blamed Awale during the trial, saying his co-defendant killed the teenagers - and threatened to kill him if he said anything.
Abukar Awale, who organised the demonstration, is himself a former khat addict.
Yahya Harun, 21, and Sharmake Abdulkadir, 21, both of Milton Keynes and Fuad Awale, 24, of no fixed address, deny a charge of murder.
BBC: Teenagers shot dead in Milton Keynes 'drug turf' dispute
Mr Awale, of no fixed address, Mr Abdulkadir, of The Fleet, Springfield, Milton Keynes, each face two counts of murder carried out with two other unknown people.
He said Mr Abdulkadir and Mr Awale had travelled to Holland to collect a gun, and all three defendants were recorded on CCTV near the location of the shooting.
Mr Abdulkadir - who also denies a charge of possessing of a firearm with intent to commit an indictable offence - said Mr Awale promised to kill him if he said anything.
Mr Awale had changed his clothing to a dark puffy jacket with a hood, and minutes before the shooting the three defendants and the other men were seen at the entrance to the alleyway, the court was told.
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