If you want to cancel one entire itn, go ahead.

If you plan on flying both outbounds and the return KEEP THE BOOKING.

1) Award tickets are RT cost. You're not getting any miles back.
2) Since it's same class, same flight just ask for the seats to be next to each other.

You've just guaranteed yourself an empty seat. Bonus.

If the flight goes into oversell, you've got two tickets to volunteer for VDB.
You also have the option of telling the CSR at check-in that hey, you've got two seats reserved and paid for because you don't like being crowded, but if it makes it easier for the airline you'd be able to swap the two seats for a larger single seat in the next class up.

I'm not seeing how this situation is a problem.