When in Mexico, I can ask for 'una torta' and get a sandwich. My wife swears that 'torta' is a cake, and she learned Castillian Spanish. I have never heard of' un emparedado'. Are these just regional differences? Or like (US) calling a sandwich a sub, hoagie, panini, whatever,etc...?
Yeah "comen" can be "they eat" or "you all eat" but "ustedes" = "you all" and if you use "ustedes comen' you eliminate "they" as a possibility. http://www.spanishdict.com/translate/comer#conjugation Look at that chart and you will see which pronouns use the same conjugation.