Our answers: are they required to sit at the table every meal? Yes. There is no eating anywhere else except for sports bottles of water near the bed at night, or popcorn on the couch for a movie or something.
for how long? Well, as long as it takes to eat! If we want to sit and have a drink or something they don't have to sit through that, but there is no sitting down for 5 minutes and then jumping up, leaving a full plate.
are they allowed to get up before they're done? Whenever they get up, they're done. Not counting getting more to drink or going to the bathroom or something. If there's a lot of food left, then I put foil over it and stick it in the fridge to be offered later in leiu of a bedtime snack.
do they have to clean their plate to get dessert or should a serving of dessert be offered with the meal? Dessert comes if they eat a decent amount of food. Also, if you request seconds, then you're expected to clean your plate because you asked for it. I'm not a stickler about it and sometimes I will say you need to eat 5 bites of xyz to be done.
can they negotiate what they get to eat? If you mean do they have input into what I cook, absolutely. They are part of the family and I cook for the whole family. SO doesn't like greens so Irarely make them, for example. I extend the same courtesy tp my kids.
are utensils required at this age? Uh......YES! at three? Utensils are required somewhere around a year and change; I'd be horrified if my 3 year old was eting with his hands.
what happens if they just won't eat at a meal and are then hungry 30min later? See above. Reheat and reserve, ad nauseum. When they go to bed I dump the plates and we can start fresh in the morning. If I had burned something or messed up something or served something they hate sometimes I'll offer peanut butter and bread even if they didn't finish their food.
We are just now "cracking down" on dd because she is just 18 months. She learned quickly that once she got down from the table, the meal was over. She loves to eat so now she stays at the table and eats her food.
This is not to say we're drill sergeants or that the kids have perfect manners. dd is insanely messy and ds isn't too neat himself. But we definitely have expectations and it's not a free for all.