While very few members of Statler and Waldorf's family have appeared in puppet form, many of them made appearances in The Muppet Show Comic Book: On the Road. Many of them resemble the two almost identically.
Statler and Waldorf's hillbilly cousins appear in the first issue of On the Road. They look exactly like Statler and Waldorf, but wear hillbilly clothes. It's implied for certain that the one resembling Waldorf is Waldorf's cousin, as upon seeing a flyer for The Muppet Show, he mentions that his cousin told him about it.
Mr. Stadler and Mr. Waltorf
Mr. Stadler and Mr. Waltorf, who appear in the second issue of On the Road, look exactly like Statler and Waldorf, right down to the clothing, and are from Little Stadwalt. Their family relation to Statler and Waldorf is unknown. They are comedy writers who work for Clint Wacky, though their material comes from Christmas crackers.
Little Stadwalt is known as the home of only two families, who are obviously related to Statler and Waldorf in some way. They enjoy the comedy of Clint Wacky, despite the fact that he constantly insults the audience.