Lots of ways to do so. I am partial to scripted approach.
From an elevated Powershell prompt it's as simple as
New-LocalUser -Name <accountname>
it will then prompt for a password and done. Rinse and repeat for each account.
All the accounts by default will be members of the Users group. To add the single account to the adminstrators group
Add-LocalGroupMember -Group Administrators -Member <accountname>