Yes, 3 people are burned alive at the end. One of these 3 was completely on conscious. Also a short flashback of another from the earlier movie is shown as well
Yes, it was once, did not look too hard, during a heated verbal altercation, and it was between similarly aged girls. If that eases it for you, you can watch safely
No fat jokes, but the ladies are overly concerned about eating carbs and 1 character only reluctantly eats 1 bite of pancake. To me the depicted fear of getting ever so slightly fatter is no better