To find what group you should do, add your DUPR rating together with your partner. Then make sure to subtract any "handicaps", -.5 for over 55 years old and -.5 for a women.
For example, a team with a 57 year old man with a DUPR of 3.5 and his daughter a 30 year old with a DUPR of 4.2. Would be 3.5+4.2-.5(for over 55)-.5(woman)=6.7, would be in the 7 combined rating division.
You can double dip on the handicaps so a 55-year-old woman would subtract 1 from her DUPR rating.