Multiple external hard drives with time machine

Good day all,

I am looking for advice on the best way to set up my externals to work with time machine.

I have 3 externals. Drive a, b, and c.

Drive a holds my work.

Drive b is my work backup

Drive c is my computer and work backup.

I want drive b to backup drive a, and drive c to backup my computer and drive a ( or b, as they both will have the same information stored).

How would I set up these drives and time machine to make this happen?

Thanks!

Heather