Each Homunculus is named after a sinful trait that dominates them the most. Plus, homunculi are immortal and are masters of an individual element or compound.
Lust: She can use her nails as super slicing weapons. I'm assuming she is some type of metal.
Wrath: Well...this guy doesn't have any homunculi powers that I know of, but he does half semi-alchemy abilities thanks to Ed's limbs.
Gluttony: Can eat anything. I'm assuming his is acid.
Envy: Can take the form of any human being. he pretty much counts as all that makes up a human body.
Vanity: Um...I don't really understand this guy's powers at all.