No you can't eat them, they are dry ice (solid carbon dioxide).
Yes.no
Sort of, depending on who is talking... As seen through a modestly good telescope, the poles show white caps that grow and shrink with the seasons. They are not solid caps of ice, metres or even...
Frozen water like earth has
Mars has two ice caps. Planum Australe (Southern) and Planum Boreum (Northern). See links for further information.