1:19 PM PT -- Law enforcement sources tell us Jacob is currently listed in critical condition.

A family featured on "Wife Swap" is at the center of a double murder investigation after one of the kids allegedly shot and killed his mother, his brother and then turned the gun on himself.

The Stockdale family, described on the show as "devoutly religious" ... appeared on an episode in 2008. Cops say on Thursday, 25-year-old Jacob Stockdale shot and killed his mother, Kathryn, and 21-year-old brother, James.

He then shot himself, and was taken by helicopter to a hospital. He's still alive, but his condition is unknown.

The family of 4 brothers made up a blue grass band with their dad. According to the family's website, Jacob was a renowned fiddle player in Ohio.

Still unclear what led to the shooting.