If you want to, I guess. A lot of Spanish learning aides, especially aimed at beginners, give ustedes as "you-all" or something of the like; the fact is, however, that "you" is both singular and plural in English and "you all" sounds a bit silly and superfluous. If you need to disambiguate, saying something like "you guys," "you people" or in this case "you chefs" or something is better.
:D however "tú" does not have a plural form per se. In Spain it's common to say vosotros which is plural "you" in the informal register.In 99% of Latin America, vosotros is said by no one and "ustedes" is used, along with its matching conjugations, for both formal and informal situations.