No hagáis ruido.

How can I know it’s not hagas?

In Spain they use vosotros/vosotras as an informal plural you, for example when talking to a group of children, or friends; in Latin American they would use hagan instead. Also hagas is in the singular you form.

Alternatively, if you mean, “How am I supposed to know which form of you to use?” then you can either add a hint for each ambiguous sentence, or do as I do with text entry, cycle through all the possibilities until you find the correct answer. With multiple choice, this, I imagine, will be very frustrating.

The issue is that there are 4 options for “you” in Spanish, depending on whether it’s singular/plural or formal/informal. And this website doesn’t note any difference between them. Unfortunate.