She sits at the kitchen table looking at photographs of her three dead IRA sons. "I lost them all, within nine months of each other," says Patsy Devine. "It's hard enough for a mother to bury one child but I buried all my boys.

"I don't know how I got through it but God gave me strength and the boys were in heaven helping me." Patsy's two youngest sons, David (16) and Michael (22) were shot dead by the SAS in Strabane, Co Tyrone, 25 years ago. Nine months earlier, her eldest son, Hughie (27), collapsed and died days after receiving a severe beating from the British Army.

"The British killed my sons and then the police tortured my family for years afterwards. I was left with three wonderful daughters and we all pulled together. We suffered so much at the hands of the state but now we're being targeted by people who call themselves republicans," Patsy says.

The Devine women are involved in an emotional confrontation with Republican Action Against Drugs (Raad), a vigilante group made up of ex-IRA members. Based in Derry and Strabane, it's been responsible for over 30 shootings and bombings in the past 18 months.

Raad alleges that Patsy's grandson, Paul Brennan (31), is a drug-dealer. "It began two months ago," says Paul's mother Cathy. "My son had borrowed my car to visit his girlfriend. When it was parked outside her house, Raad threw a pipe bomb inside which exploded, destroying the car.

"Raad gave us no warning. They could easily have come and asked us about Paul, and heard the truth. Paul smokes a bit of blow but he doesn't deal drugs. We are horrified at the very suggestion that he does. This is putting terrible pressure on us all, particularly my mother."

A stroke has left Patsy paralysed down the left hand side of her body and her stomach was removed after she was diagnosed with cancer. She needs regular medical treatment. "Cathy used that car to take me to the doctor's and to the hospital," says Patsy.

"I don't have words strong enough to describe how I feel about Raad. They aren't republicans and it hurts me to hear them claim they are. They should stop using that name. They bring nothing but shame to republicanism. Raad are telling lies about Paul. If he's this big drug dealer, why does he never have a penny?"

After lengthy dialogue through intermediaries, Raad agreed to meet the Devines last week but the group then pulled out of the meeting. "They're cowards," Cathy says. "Why don't they have the courage to explain to us face-to-face why they targeted Paul or are they afraid of a few women?"

Local Sinn Féin MP Pat Doherty has strongly condemned Raad. The Devines are also being supported by former IRA and INLA prisoner Willie Gallagher of the Irish Republican Socialist Party (IRSP), the INLA's political wing.

Gallagher says: "I've known the Devines all my life and it breaks my heart to see Patsy sitting crying because of Raad's disgraceful behaviour. I joined the IRA as a teenager with Patsy's son Hughie. We operated together and were on the run together.

"I know how Patsy grieved after she lost Hughie, David and Michael. Following Raad's claims, the IRSP investigated Paul Brennan. We found the allegations to be false but, even if they were true, it's immaterial. Out of respect, the family of three dead IRA volunteers deserved to be approached before Raad took action. Any 'evidence' should have been put to them."

Gallagher says he made his opinion known to Raad: "I met them and they agreed that the family should have been approached first. They promised to meet the family but then reneged on that."

He says the Provisionals have "lost control of Raad" which is made up of "ex-punishment squad members". While the Sinn Féin national leadership is strongly opposed to Raad, Gallagher says a handful of local mainstream republicans are involved in the group.

He says "a veiled threat" was made by a Strabane Sinn Féin member whose name is known to the Sunday Tribune. This individual allegedly warned that if the Devines came out publicly against Raad, Paul Brennan would be shot or put out of the country.

Several Raad members are also allegedly involved in a republican band in the North-West. When a Provisional IRA representative met the band and told them such dual membership was unacceptable, some of the band members walked out.

Raad's supporters say it's effectively tackling the drugs problem which has increased dramatically since the IRA ceasefire. However, another source claimed the group were "a bunch of extortionists and gangsters" who taxed drug dealers by taking money and cars from those who co-operated, and targeting those who didn't.

Back in her kitchen in Strabane, Patsy Devine says she just wants any threat against her grandson lifted: "I lost three sons; nobody should touch a hair on the head of my grandson."

Michael and David Devine were returning weapons to an IRA arms dump when SAS soldiers, hiding in the field, opened fire without warning on the brothers and another IRA member, Charles Breslin, in 1985.

The SAS fired 117 rounds. Michael Devine was shot 28 times. A pathologist described his wounds as "almost beyond interpretation". The IRA trio didn't return fire – two of their guns had safety catches on.

Patsy's daughter Antoinette says: "We had an exhibition recently to mark the 25th anniversary of my brothers' killings. David was still at school and we displayed his school books. Michael loved snooker and we had his cue and the trophies he'd won on show.

"We had both boys' coats and shoes too. The anniversary was like going through their deaths all over again. Why can't Raad just leave us to live in peace? We've been through enough."