Forgot a few more:
Johnny Fiamma and his "Ma"
Emmett and Ma Otter
Hattie and Charlie Muskrat (also from EOJBC)
There was also a family of squirrels in the "Emmet Otter" talent contest doing a gymnastic act of some sort...their mother can be seen gushing over them in the audience after they're done. (Pardon the stretch!)
Let's also not forget the Sesame Street humans, after all, they were (the voices of) Muppets once:
Gordon, Susan & Miles
Maria, Luis & Gabriela
(Is it just me or do you think they'll turn Miles and Gabriela into the next Maria and David?)
There was also an ep of TMS where Statler was babysitting his grandson (who takes after Statler in the insult department...at least the kid isn't gonna be bald and toothless forever!)
Other family relations:
Big Bird and Granny Bird (NOTE: Big Bird also mentions some of his relatives in the ep where Madeline Kahn and Richard Hunt play bird watchers, one of whom is named Floyd.)
David (Northern Calloway) and his grandma (thanks to Count Von Count who confirmed that it IS Clarice Taylor, who also played Bill Cosby's mother in "The Cosby Show", that's been eating away at me for QUITE some time!)
Waldorf and his wife Astoria (Statler in drag...maybe Astoria is Statler's sister, and Waldorf was the only available sucker...er, bachelor he knew)
Scooter & Skeeter (Muppet Babies, although she would've made a great adult Muppet!)
Mr. Hooper and his brother Arnold (played by the late great Jack Gilford)
And contrary to what Miss Piggy says, Kermit is not Foo-Foo's "dada"!