In a separate hearing linked to the trial, two other members of the group admitted attending a terrorist training camp.
Sentencing will take place at a later date.
"Hamid and Ahmet are dangerous people who between them carried out the recruitment, grooming and terrorist training of young men," said Peter Clarke, assistant commissioner for specialist operations at London's Metropolitan Police.
Prosecutors said Ahmet and Hamid prepared the men for jihad, or holy war, by organising terrorism training disguised as camping or paintballing trips in rural locations around Britain.
An undercover officer who helped secure the convictions once heard a conversation in which Hamid boasted: "Fifty-two, that's not even a breakfast for me", referring to the July 7 attacks.
"Hamid directed his recruits through military exercises, teaching them how to defend themselves against armed ambush. This was not innocent activity taking place on a camping weekend," said Clarke.
"Hamid's links to men convicted of carrying out the (July 21) attempted bombings in London shows the depth of his involvement in terrorism."
Britain's security services say numerous Britons have travelled abroad, mainly to al Qaeda camps in Pakistan and Afghanistan, to learn militant training skills, but this was the first case of its kind involving training in the UK.
The jury were shown pictures of the men practising firing positions using sticks instead of guns, pretending to throw grenades, crawling through streams and carrying out other paramilitary-style exercises.
The day after the July 7 attacks, Hamid sent a phone text message to one of the July 21 conspirators saying: "We fear no one except Allah. We will not change our ways. We are proud to be Muslims".
The court also heard that when he was arrested in October 2004 at a stall in the capital's Oxford Street shopping area, he told police he was "Osama bin London" and claimed to have a bomb.
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