none of those are yes or no questions also since he ordered it and the waiter SERVED IT...

had the men been to the resteraunt before? with eachother? or by there self?
had they sat in the same place, if yes.
did the old man know anyone that worked at the resteraunt

They had never been to the restaurant before and the old man did not know anybody who worked there.

Was the old man a smuggler?

Was the young man a smuggler?

Was the gun the young man shot with a pistol?

Did the waiter deliver the seagull to the table?

Is there something to do with the marina?

No no doesn't matter yes and no gj spotting the false lead there.

Did the waiter have something to do with it?

no the waiter had nothing to do with it ( other than bringing the food)

did the old man whisper a question to the waitor?
did the waitor respond to the whispering in question?
Is anybody at the table alergic to seagull?
are the old man and young lad related?

no no no and yes

Is seagull a code for i'm going to shoot you in the face with this here gun in my trench coat?