(the question is aimed only for FMA03 and not FMAB as suggested from the title and contains uncovered spoilers for the anime)
I have a little trouble that the homunculi called after the 7 sins by FMA03 way, and I will explain.
In the FMA03 anime homunculi are created by failed human transmission, if that so, what makes them go by the title of the "7 sins" as Envy, Pride Lust an etc., it's hard to me because: if there were than more 7 people in the world trying human transmission what they would called? second what makes them to be after the 7 sins in their behaviour if they are "failed" and didn't deliberately created? my main issue is, why they needed to be called after the 7 sins anyway? what for?
I thought this through and this is what I got:
I could have said that Dante made them that way by make them eat the red stones and by that they got those emotions and behaviour, by Dante management, it could were the truth if not for the creation of Wrath that didn't made to be look like human by Dante and his behaviour was "Wrath" from it's origin and didn't grow up by intervention. (which is another question not for here, how it grew up to be human shape without red stones)
I could say that is only Dante way to call her fellow homunculi after the 7 sins, but in this way I will have to say that she couldn't except that Izumi's homunculi will be Wrath or any other sins to go after some pattern unless we will say the first answer.
I could say to answer for both of those answers that Dante knows that the spirits for the homunculi behind the gate can be only one of the 7 sins, but this one not only needs hard evidence but hard to say since there can be 2 or even 3 Pride or Lust.
Anyway I would glad to be enlighten or I missed a thing.