Fiance's cousin wants to stay 5 nights at our place

I'm the only one working at the moment and we're low on money. His cousin makes me nervous because last time he was here, his dad (uncle) and him smoked a blunt in my fiance's and I's bathroom. And my fiance joined in because it was "too cold" outside (this happened in the winter) and smoking in general in the house is against our apartment lease. Normally my husband and I smoke outside but never inside the house. I feel nervous about something happening like that again but i feel bad because I'm supposed to be comfy around his family. But we're severely low on money and 2 people is enough for food but 3 is struggling for us with just me working. I already asked my fiance to wait on his cousin staying because we need to talk about it first.