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Not automatically.
The billing date for each line is set according to the day each plan is activated.
All plan purchases and activations made on the same day will have the same billing date.
So for example, if you are a new customer and purchase and activate 3 lines on the same day, you will have the same billing date for all your lines and 1 invoice to cover all lines.
However, if you decide to merge some family members' existing lines into your own account, then all the lines will retain the existing individual billing dates. The billing dates will not sync.

If you would like to add new lines to your account for people who are not already Tello customers, and you really need to have the same billing date, then the best thing to do is add the new lines on the morning of your existing billing date.