Lloyd Campbell, 73, and Allen Nicholas Jr., 63, were found inside a detached garage on the unit block of E. Monroe Street on Tuesday morning.
The Gloucester County medical examiner determined that the deaths were accidental, the prosecutor's office said. No further details about how the poisoning happened were released.
Campbell was the owner of the property. The garage they were in is part of Campbell Towing and Auto Service.
The entire Campbell family is well known in Paulsboro for their work.
"My great-grandfather, to my grandfather, passed it down to my uncles," a relative, Andre Campbell, told Action News earlier this week. "My stepfather, he was already a great mechanic and he married into our family. Just added to the legacy of hard-working blue-collar people."