The Mannan family – including three children aged 11, five and one – are understood to have cross into Syria in May 15.
It is thought they crossed into the war zone to join ISIS after landing in Turkey on the return trip from visiting relatives in Bangladesh.
Two months after arriving in Syria, the family released a statement declaring their full support for the murderous jihadi death cult.
Four years on it is claimed that all 12 of them have now been killed in fighting and airstrikes, reports Mail Online.
Relatives left behind in Luton revealed that all those who made the trip have been killed in Syria.
“It’s a tragic end and we have drawn a line under it all and are now trying to get on with our lives”
Muhammad’s son Shalim
Three of the grown up sons from the Mannan family were killed while fighting for ISIS.
Seven more relatives – including the three children – were reportedly all wiped out in an airstrike.
Elderly parents of the family – Muhammad and Minera – both died of natural causes in the terror group’s capital of Raqqa.
ISIS has been almost utterly destroyed as a state, but is still a threat due to its web of terror networks worldwide.
Muhammad’s son Shalim, from a previous marriage, said: “They are all dead. It’s over, finished.
“We had been trying to find out for some time what had happened to them and it was only confirmed to us recently from Syria.
“It’s a tragic end and we have drawn a line under it all and are now trying to get on with our lives.”
The 75-year-old family patriarch reportedly died in Raqqa shortly after arriving, while Minera also succumbed to cancer.
His two youngest sons, Mohammed Zayd Hussain, 25 and 19-year-old Mohammed Toufique Hussain both died in the battle for Raqqa in October, 2017.
It is claimed the rest of the family managed to escape the terror capital, and ended up held up in ISIS’ final stronghold of Baghuz.
Another son, Mohammed Abil Kashem Saker, 31, was shot and killed during fighting with the US-led coalition.
The remaining members of the Mannan family perished in an airstrike while trying to flee Baghuz.
Rajia Khanom, 21, son Mohammed Saleh Hussain, 26, and his wife Roshanara Begum, 24, their three children and another daughter-in-law, Sheida Khanam, aged 27, all died.
Muhammad’s cousin Abdul Khalid said: “From what we’ve been told they were trying to get away from Baghouz and make their way to a camp, like so many other people were trying to do at the time but there was a lot of bombing going on and they got caught up in this.
“They were all together, that’s all we know. We are not sure if they were in a house or out in the open but the fact is that they are all dead.
“The details of how they actually died don’t really matter to me.”
It is said Muhammad and his family’s death is known by many members of the congregation at the Bury Park Mosque in Luton.
The Mannan Family released a statement declaring their support of ISIS – hailing the vicious state as “free from corruption and oppression”.
It said: “All 12 of us and why should this number be shocking, when there are thousands and thousands of Muslims from all corners of the world that are crossing over land and sea everyday to come to the Islamic State?’
Muhammad is the oldest Briton to have ever travelled to Syria – but pals said at the time been said they were “tricked” into going to the state.
Abul Hussain, chairman of the mosque said: “He was a lovely man who was really devoted to his family.
“When he went to Syria we were all shocked because we couldn’t believe that he was capable of something like this.
“It was not the Muhammed we knew.”