Does the monthly bill for an iphone include the data usage?

I want to get an iphone 5c (it would be added to my families plan of unlimited texting and minutes, with 6 gb of data) and on verizonwireless.com it says it will be $40 monthly (before taxes.) But there's also a fee for our family that is $70 for the 6gb of data each month. Is that added on to the monthly $40 per persons phone? Also, if I just pay $40 or so each month my parents still have to pay for the whole $70?

I guess I'm asking if this is how it goes each month assuming we all have smartphones:

Dad: $40

Mom: $40

Brother: $40

Me: $40

Data plan: $70

It does

The assumption you made is correct.

Adding more people to the line does not change the $70 data plan that your parents are already paying for, it will simply add the $40 for your phone.

So, if your parents are currently paying about $190 a month now (before taxes), then they'll be paying $230 a month when you get added on.