The eldest of three sisters found dead in a submerged car last month was in a forbidden relationship with a young man before her death, according to a relative, who says the 19-year-old girl had clashed with her family earlier this year.

Zainab Shafia's body was discovered with those of two younger sisters, Sahar, 17, and Geeti, 13, on June 30. Also found dead in a submerged car in the Rideau Canal was Rona Amir Mohammad, a 50-year-old woman now identified as their father's first wife.

Father Mohammed Shafi, wife Tooba Mohammad Yahya and their son Hamed Mohammad Shafia, 18, have been charged with first-degree murder and conspiracy to commit murder in connection with the deaths.

Kingston police are investigating the possibility that the three girls and the woman were victims of a so-called "honour killing."

Rona's brother says that the family was locked in conflict and that the eldest daughter's romantic relationship with a young Pakistani man may have been a contributing factor in the tragedy.

"The parents of this girl did not want her to marry a Pakistani boy who didn't have any money. They didn't want that," relative Wali Abdali, who lives in France, told CTV Montreal on Friday.

Rona, who had previously been identified by the family as both an aunt and a cousin, lived with her husband, his second wife and their seven children at the family's Montreal home.

But the family arrangement was causing strain, according to Abdali.

"They didn't have a good relationship. The other woman didn't want my sister to stay in the house with them," he said in French.

The father reportedly took a second wife after it was found that Rona couldn't conceive. The marriages took place in Afghanistan in the late 1970s and early 1980s, where it is legal to have two wives.

According to Zarmina Fazel, who is the aunt of wife Tooba, Shafia is a smart businessman who has worked hard to build a life for his family in Canada.

Shafia owns at least three business, and last year, he bought a retail mall in Laval, Que., which is worth around $2 million, CTV Montreal reported.

Shafia was also building a large family home in a gated community in Brossard, a suburb east of Montreal.

Originally from Afghanistan, the family lived in Dubai for 15-years before coming to Canada two years ago.

Community reaction

Another relative defended her family members, in an interview with the Toronto Star.

But Zarmina Fazel, the aunt of the girls' mother, Tooba Mohammad Yahya, has alleged that the four victims died as part of a suicide bid by the eldest daughter, Zainab.

"Zainab was not normal," Fazel said. She defended both parents, saying that father Mohammed is "a very honest man" and that the teens' mother was "not that kind of person."

The three accused are being held in police custody until their next court appearance on Aug. 6.

The whole family was on the way back to their home near Montreal, in Saint-Leonard, Que., around the time the submerged car was discovered. They had been returning from a trip to Niagara Falls.

As rumours surrounding the deaths continue to circulate, Ihsaan Gardee, spokesman for the Canadian Council on American Islamic Relations (CAIR-CAN), said the term "honour killing" is troublesome.

CAIR-CAN is a non-profit organization whose mandate is to strive to be a leading voice that enriches Canadian society through Muslim civic engagement and the promotion of human rights.

"With regards to the term honour killing thrown about, all Canadians soundly reject killing, by whatever name -- a killing is a killing," said Gardee.

The term has been used to describe other high-profile cases in Canada, including the 2007 death of Toronto teenager Aqsa Parvez, who was allegedly killed by her father and brother after she refused to wear the traditional Muslim headscarf.

But Gardee said using the phrase sends the message that "the killing of women and children is the exclusive monopoly of any one faith or culture or ethnicity."