This could be translated as "at the table" or "sitting at the table." The Greek style of eating at a feast was to lie on a couch and prop oneself up with the left arm on some pillows.
## to his disciples ##
"to Jesus' disciples"
## Why do you eat ##
The Pharisees and scribes used this rhetorical question to express their disapproval that Jesus' disciples were eating with sinners. The word "you" is plural. This could be translated as "You should not eat with sinners!" (See: [[rc://en/ta/man/translate/figs-you]])