Propylene Glycol: I understand this makes soap soft and has some moisturizing properties, but when would this be added to the soap? It is listed first in many of their products.

Sodium Stearate: I have found on the web that this is made from tallow, but the maker lists the soap a "vegan". At thechemistrystore.com, it says something about "palmetic", so is this made from palm oil?

Sodium Palm Kernelate: self-explanitory

Sodium Lauryl Sulfate: is this made from coconut oil?

Tetrasodium Editronate: listed last on most of their soaps. What is it and why is it in there?

Lastly, when working with a number of fats and oils, like mixing palm oil, palm kernel oil and coconut oil (as above), how do you come up with the amount of lye to use?

I am researching this and will probably try my hand at soapmaking soon. Thanks for your help!