I haven't personally messed with chairs yet, but I have used the Banquet table before & I've noticed that it has limited range & only affects those within it's range when the progress bar resets (this seems to be the point the effect of it activates & applies the "well-fed" buff to those around it). Are the chairs close enough to the props you are attempting to acquire the affect from?
I can see where your concern on this would be, given you might be using those chairs to keep them in place while waiting for the effect to trigger (given they won't typically go right to it; I've only seen rare cases where it seems a character would go right to it when it's ready to trigger). I personally have been having to pick them up & take them over to the table & hold them there until it went off to make certain they would get the buff (either by leaving a dialog window open with them or by doing the dirty with them at the table as a prop action), then repeat as necessary with other characters when needed (what I do find as odd however is the application of "well-fed" through the Banquet table doesn't negate the Hungry debuff if that character has it).