“is the limit on growing plants 4 per household or 4 per person? like if 3 people lived at one dwelling can they grow 12 plants?”
You are able to grow 4 plants per household. For example 6 people live in a dwelling, you are still only legally able to have 4 plants within the household. If 3 people live in a dwelling, you can legally still have 4 plants.
Keep in mind if you are renting, your landlord will also typically have to approve the growth of the plants on site.