Mike and Jeff are two of the Flippo children acknowledged to exist in Gerosha Prime, Despair Gerosha, and Classic Gerosha. As of Comprehensive Gerosha, their existence is no longer canon. They were hinted at existing in the end of The Battle for Gerosha in its 2005 form, and were to be alluded to in Ciem 2 in 2009. However, they were never seen on screen.
Some time after Erin was officially adopted by Stan and Shalia, Mike and Jeff were born as identical twins. They were soon followed by Vince (later renamed Tom,) as well as by Jason and Tanya. Finally, the triplets were born: Candi, Miriam, and Marina. They would grow up to run a party supplies store together, along with their wives. Since they would have nothing to do with Candi, little is known about their lives after Candi leaves Gerosha behind. In Ciem 2, Candi was to remark about how "useless" her brothers were, given their total unwillingness to be there for her.
Mike and Jeff were several additional children given to Stan and Shalia as part of an attempt to fulfill Stan's Family Aspiration desire to "have ten children." The baby count ended with Marina, however, putting Stan's count at nine since Ploribus Philippine was deemed as "not counting." Little practical use was found for Mike and Jeff at all in Gerosha Prime, and that carried over into Despair and Classic Gerosha. In Despair Gerosha, their siblings Jason and Tanya were written out due to no idea of how to utilize them in-story. By Comprehensive Gerosha, Candi's siblings were reduced to a Reily, Erin, "Darius," Miriam, and Marina. Not only were Mike and Jeff written out, so also was Tom Flippo.
Even Marina barely survived into Cataclysmic Gerosha's continuity, nearly being written out and making Candi and Miriam twins rather than triplets.