In The World of Ice and Fire, we are introduced to few historical Tully characters, which are:
The coincidence doesn't end there. Tully family ruled Riverlands. Riverlands has three Forks contributing to River Trident:
Guess what colors Kermit, Elmo and Grover are ?
This is definitely not just a coincidence.
ASOIAF wiki confirms:
Kermit, his father Elmo, and his great-grandfather Grover are references by George R. R. Martin to The Muppets.
But there is no reference added as to where exactly did GRRM confirm that was the case. Googling doesn't yield any statement from GRRM or his team. Has GRRM ever confirmed that he was indeed influenced by the beloved puppet characters while naming the Tully Lords?