You want to create copies of a standard family in Content Center.
You want each copy to have a different material.
In addition you want that any change you make to the first copied family will apply to the other copies as well.
In order to achieve this, all copies need to be linked to the first copied family.
So, starting from one standard family and using the Material Guide, you need to create first an independent copy with a different material.
Then, from that family copy, with the Material Guide, create the other copies linked to parent family and assign to each copy a specific material.
You can see the procedure in the video below.