Family trying to open my parcels

I'm 21 but I still live at home with my parents/sister when I'm not at uni and every time I order a parcel to home they just keep asking me what it is over and over again, asking if they can watch me open it or asking if they can open it for me if I'm not in when it gets delivered. I know I live in their house but I should at least be entitled to that small amount of privacy to order what I want as a literal adult. How do I tell them to mind their own business without being overly rude