How do I re pot my many baby cacti?

I bought a cactus "egg" in Arizona. It came with a miniature egg shaped greenhouse, soil, and three different varieties of cacti: saguaro, barrel cactus, and prickly pear. They are almost half a cm high, and will need re potting. How should I treat them? How shallow are their roots? I'm from Alabama, so these little cacti are all I have left from Arizona but memories and a t-shirt. Thanks!