Visible only has single line accounts so each person in your family that wants to switch to Visible will need a separate account. You can keep your number by porting it into Visible. If you have a newer iPhone or an Android phone that is capable of eSIM you can do the free 15 day trial and see if you like it first. The trial is the base plan so it is deprioritized on data.
If you are looking for a family or group plan you would need to look at other carriers for that, I see US mobile mentioned a lot on Visible's Reddit page.
