One has been named as an al-Qaeda suspect who left the family's Birmingham home years ago and the other has been described as gentle and polite.
British security sources believe that one of the 23 suspects being held in custody is al-Qaeda's leader in Britain.
British airline passengers are continuing to suffer chaos from the fallout of the investigation as airlines cancelled almost a third of flights from Britain's busiest airport Heathrow.
British Airways said it had scrapped 30 per cent of flights from Heathrow on the instructions of airport operator, the British Airports Authority (BAA).
A British Airways flight from London to New York turned around mid-flight and returned to London's Heathrow airport after a mobile phone started ringing.
"A mobile phone was located on board the aircraft which none of the passengers appear to own," a British Airways spokeswoman said.
"The captain assessed the situation with the BA security team at Heathrow and it was decided that it was safe to continue. However, the captain decided to return to Heathrow as a precaution,” she said.
Reid warns
The US Department of Homeland Security has also downgraded the threat level for inbound flights from Britain to "code orange" from "code red," its highest security risk alert.
British Home Secretary John Reid said the threat is a chronic one and it is a severe one and that there could be another attempt to target airlines.
"We think we have the main suspects in this particular plot,” Mr Reid said.
“But I have to be honest and say on the basis of what we know there could be others out there, perhaps people we don't know, perhaps people who are involved in other plots,” he said.
“So the threat of another terrorist attack in the United Kingdom is still very substantial."
Reid repeated the assertion, made before by police, that Britain has foiled four major plots since the July 7, 2005, London transit bombings, and said police were conducting about 24 investigations.
Police suspect that suicide bombers would have been put on board up to 10 US transatlantic airliners at British airports.
They were to be armed with electronic detonators and with liquid explosives disguised as harmless drinks.
Reports of more plots
In a front-page report, the Sunday Times said while it could not name the suspect due to legal reasons, MI5 officials believe he is "the senior figure in a British terror network involving Kashmiri, north African and Iraqi cells".
It is suspected he was "instrumental" in sending the ringleader of at least one previous British plot to a training camp in Pakistan, according to the Sunday Times.
The newspaper also revealed concern within the security services that more suspects may be at large, including "at least two" who escaped during raids last week.
But they believe they have arrested "the ringleaders, the technical experts and the foot soldiers" behind the plot, an unidentified police source was quoted as saying.
The Observer, quoting security sources, said "up to two dozen" investigations were now under way in Britain, and that MI5 "used a mole from within the Muslim community" to infiltrate the alleged airliner plot.
The News of The World said the security services are "secretly battling another 30 Islamist murder plots" - some single-cell outfits, others "multi-cell groups plotting attacks of incredible complexity".
It also said the "mastermind" in Pakistan of this past week's thwarted alleged plot was Mati Ur Rahman, "a top al-Qaeda figure", and that eight of those arrested in Britain were due to board flights as suicide bombers.
The Mail on Sunday, quoting a government source, said "a dozen terror plots" were under investigation by MI5.
Brothers implicated
"No-one should be under any illusion that the threat ended with the recent arrests. It didn't," Mr Reid told police chiefs. "All of us know that this investigation hasn't ended."
Attention has focused on the role that the brothers Rashid and Tayib Rauf may have played in the alleged plot. Their father, Abdul Rauf, emigrated to Britain from the Mirpur district of Pakistan several decades ago, and his five children were all born in Britain.
Rashid Rauf was arrested about a week ago along the Pakistan-Afghan border, and Pakistani officials have named him as a "key person".
They allege that there is evidence that links him to an "Afghanistan-based al-Qaeda connection" but have given no details.
His 22-year-old brother Tayib was taken into custody in Britain during the sweeps that nabbed 24 people there, and there were unconfirmed reports a third brother may have been detained.
British police probe
British authorities have released little information about the brothers, or the course of their investigation into the alleged plot in general.
There were no briefings for a second straight day and senior government figures stayed largely out of sight.
British police have released one of the 24 people originally arrested while no charges have been filed yet against the other 23.
Under tough new anti-terrorism laws, authorities can hold suspects up to 28 days without charge, but pressure is likely to mount for police to disclose at least some of the evidence.
In Pakistan, where authorities are anxious to put a positive spin on a story, officials spent the weekend leaking details of the role the country played in cracking the case.
Pakistan is questioning at least 17 people, including Rauf and one other British national whose name has not been released.
A senior Pakistani security official said Rauf's arrest prompted an accomplice in the southern city of Karachi to make a panicked phone call to a suspect in Britain, giving the green light for the airliner plot to move forward urgently.
"This telephone call intercept in Karachi and the arrest of Rashid Rauf helped a lot to foil the terror plan," the official said.