Your family is giving you a responsibility in the family business, and it's a fairly serious responsibility, at that. It shows they obviously think you're mature enough to handle it.
You should honestly be happy they find you mature and responsible enough to handle the business bills, yes it's tedious but it will give you important skills later in life and make it easier for you to get a job later as well.
I started working at our family business, and getting paid, at 12, but I worked unpaid there since it opened when I was 8. It was usually only $20 a day or less, but now I have the luxury of having a decent paying job with no stress of fearing I'm going to lose it.