How can you tell a male iguana from a female iguana?

i might adopt two iguanas i havent seen them yet but the people i am getting them from dont kno what genders they are. i would like to kno when i get them. so please help! pictures would also be a great help! also if one is male and one is female can i keep them in the same cage and would they mate? or can i get an iguana neutered? they are 2.5 years old idk if that helps or not! but thanks!!!