"They don't eat cookies."
Translation:הן לא אוכלות עוגיות.
Sometimes we write word like ugiya with 2 yods because the two sounds has a yod:
עוגי + יה
Yesss... you're right. That was an old comment. I didn't know it well back then.
What or who is the object of the action? Here it's eating, whose eating? Plural females, הן. So you'd need plural feminine. If it was mixed, this female thing & that male thing or if it's plural male, even if it's written like female (אירה, יין; wine, Lion) then you need male plural.
This time I used אוכלות and it said it was אוכלים which is what i used the first time and it said it was אוכלות.