Hassan and Moatasem Deeb "were killed Friday in a rebel assault on the Abu
Zeid army checkpoint near Qalaat al-Hosn" in Homs province, Sheikh Mohammed Ibrahim told AFP.
Their deaths have devastated their parents, who had already lost a third son Rabih to sectarian fighting in Tripoli last year.
Sheikh Mohammed said Moatasem, 18, blew himself up in a suicide car bomb at
the checkpoint, and Hassan, 21, died in the assault that followed.
The youths apparently did not die in vain, as the assault on the checkpoint
succeeded, said the cleric.
Cousin Jihad Deeb said that, although the youths had long been "deeply religious," the news of their deaths hit the family hard.
While still in Sweden just a year ago, Hassan had started his university studies. And had he stayed in Scandinavia, Moatasem would have started his degree this year.
"But they left everything and travelled back to Mankubeen, where their parents have been living for two years now," said Jihad.
Established to host families from Tripoli during a 1955 flood, Mankubeen later became home to people too poor to afford life in the heart of the northern port city.
Today, Mankubeen is an impoverished area that frequently gets dragged into
sectarian clashes pitting Sunnis from the Bab el-Tebbaneh quarter and Alawites
from neighbouring Jabal Mohsen.
Tripoli's sectarian clashes erupt frequently, and their intensity has grown as a consequence of the war raging in neighbouring Syria.
Sectarian tensions in Tripoli see Sunnis generally supporting Syria's rebels and Alawites, the Shiite spinoff group to which Bashar al-Assad belongs, backing the Syrian president's regime.
Eighteen months ago, Moatasem and Hassan's brother Rabih was killed fighting in one of those clashes.
The commitment to jihadist activities among family members goes further.
In 2007, one of the youths' uncles was killed fighting alongside Islamists in a fierce battle against the Lebanese army in the Palestinian camp of Nahr al-Bared.
Another uncle is in jail in Germany over ties to Al-Qaeda.
Once they returned to Mankubeen from Sweden, where they had lived for several years, the young men "decided to cross the border and join Jund al-Sham", said the sheikh, who stressed that no one knew of their plans.
Jund al-Sham is an independent jihadist group set up in 2012 and led by Lebanese radicals.
"Moatasem travelled first. He went to Qalaat al-Hosn eight months ago. Hassan joined him two months later," Ibrahim added.
Jihad Deeb said "they had no work, and they lived in a poor area that has no state support. Most of us are not radicals, but you see many Al-Qaeda flags in Mankubeen."
Asked why he believed his cousins joined the rebels, he added: "Hassan and
Moatasem really believed that Sunnis must fight there.
"But their father and mother are devastated. The father is near emotional
collapse. And you can imagine how their mother feels; she has lost three sons."
The family was due to receive condolences from guests on Saturday, who
would "congratulate" them for their sons' "martyrdom" in Syria, said Ibrahim.