You're overcomplicating this hugely. It's much simpler to burn the alcohol within the astronauts, converting it to a small amount of heat, CO2 and happiness.
You missed the key distinction here, ethanol is not the greatest substance, but is relatively safe for animals. Other side chain alcohols metabolize into byproducts like formaldehyde and well, are highly toxic. This whole distinction is the basis for the sale of "denatured alcohol" / "wood alcohol" and its much cheaper price.
"In some countries, sales of alcoholic beverages are heavily taxed. In order to avoid paying beverage taxes on alcohol that is not meant to be consumed, the alcohol must be "denatured", or treated with added chemicals to make it unpalatable."
Ethanol is normal drinking alcohol. You are thinking of methyl alcohol, methanol.
As little as 10 mL of pure methanol, ingested, is metabolized into formic acid, which can cause permanent blindness by destruction of the optic nerve. 30 mL is potentially fatal, although the median lethal dose is typically 100 mL (3.4 fl oz) (i.e. 1–2 mL/kg body weight of pure methanol)..
