The translation su agrees in number with the noun which it modifies; their is translated by su, sus, depending on what follows: their father/mother su padre/madre; their books/magazines sus libros/revistas. For their used with parts of the body,
Here is a selection of useful words and phrases you will need in real-life situations while you're visiting Spain and other Spanish-speaking countries...
Pulque is a thick, white, Mexican alcoholic drink made from fermented maguey juice; the sacred drink of the Aztecs. It is drunk without being aged, sometimes with added fruit or vegetable juice. Pulquerías are bars where it is drunk.