Just an idea: you can get the packets from the restaurant and can go to some public place (Dhanmondi lake is in just a few minutes walking distance from there, 4-5 people can volunteer to carry the packets) in case if you don't find seats. We usually do meetup in public place and with a banner and good location, it would be easy get others' attention! I am aware that it also has challenges, but it's better than seating somewhere than eating while standing.
T.