"Sie isst" says "She eats". It's "essen" because here "sie" means "they" (plural), and "essen" is the form of the verb "to eat" that goes with plurals.
why no sie isst? why essen???
Here " SIE" means THEY, plural, so it is " Sie essen"
Why not Ihr esst?
I believe "Ihr" is better translated as "you all" or "y'all", an informal plural you.
I am not a native speaker, but I believe that "Ihr" is not a valid translation of "they".
why not Die essen?