How do family plans work: do you all share data? If each person has his/her own, what happens if some are over, or some are under? What happens in general if you don’t use all of your data?
There isn’t a family plan. As such, everyone one has their own cellular data that is not shared. You can’t go over. Data just stops, like running out of gas in your car. You can buy more data by changing your plan to a larger data plan and then changing back to a smaller plan before your next billing if this is just a temporary need for more data.
Any unused cellular data is forfeited.
For families that consume a bit of cellular data, you probably get a better deal with the big four or one of their owned subsidiaries like Cricket, Boost and so on.
I just want to add to @marshallh 's correct answer that you can create your own plan by managing the data allocation for each family member. This can actually be cheaper than a conventional family plan because lots of people don’t need cell data at all. Take a family of 4 for example. 3 can be on the $15.00 plan and one on the $20.00 plan. $65.00 for 4 smart phones is less than I used to pay Verizon for two dumb flip phones.
Or one phone can be with a different carrier and the others with Republic. This has the added advantage of not putting all your eggs in one basket.