Carl Peterson (Ron Raines) was not Jeffrey's uncle - he was his 'mentor' and benefactor, essentially his adoptive father. Peterson was a very well-known business tycoon and philanthropist whose arrival in Llanview was the talk of the town at the end of OLTL 2.0, but it was quickly revealed he was part of the Triskelion cartel - the 'tattoo organization' that had masterminded Victor's abduction and was threatening Todd and his family. Peterson was the emerging new villain on the scene, and quickly began attempting to romance the newly-single Dorian.
Jeffrey was working for Peterson and the cartel in secret while posing as Viki's protege - he was drugging Clint to make him unstable. Peterson was also the brother of Alison Perkins, who he'd used to imprison Victor, and who he sent to attack Clint in the 2.0 finale.
We never learned who Jeffrey's biological family was, but as they were invested in the character I expect it would've been someone important.