You can select , copy and paste contacts from group 1 to another group 2 see Mac keyboard shortcuts Mac keyboard shortcuts - Apple Support
Clarify , how are you downloading half of the contacts from iCloud are they created with gmail or other services , you can add gmail accounts in Mac internet accounts .
Add an internet account - Apple Support
Change Internet Accounts settings on Mac - Apple Support
Use your internet accounts on Mac – Apple Support
Once done , in Mac system preferences > check mark the box of contacts Set up and use iCloud Contacts - Apple Support
The gmail contacts will be saved address book , finally select , copy and paste contacts .