Answered question
Is it possible to have multiple lines in 1 account? With everyone sharing the data? Like a share everything plan
You can have multiple lines on an account but I don't think you can share data. Each plan needs a data plan. You can gift data from one plan to each other though.
Other answers
I think you can have 3 line in the same account but you cant share data. But you can give data to the plan who need it.