Nibbles, 6.5 5.5 bytes (11 nibbles)
Edit: -2 bytes by using transpose, inspired by Jonathan Allan's Jelly answer
|$>2`'=~$$
|$ # filter each word int the input by
=~$ # group the letters by
$ # themselves,
`' # transpose this list of lists,
>2 # and remove the first 2 elements
# (so if there is at least one letter
# present >2 times, the resulting
# list will have nonzero length)