Me, my wife and my 2 kids have their own PC´s. What license do I need?
You have two options:
If you are administrating all PCs and the other family members don’t want their own account you can use a 1 user license.
If your wife or kids do not want to share an account with you, especially under the consideration of the online backup options, you can then have a multiple user license and every user will have his/her own account.