I am in a similar situation with needing to cancel an award that costs as much or more to cancel than to throw away.

If flying economy, then HKG-MAA costs 10k AM, which is the same exact cost to cancel the award and redeposit the miles (you could also pay USD 120 cash to get the miles back, but that isn't necessarily a better option if the miles expiration don't get reset for another year (it could be less than a year)). If you cancel, you get your taxes and other fees back. Another option is to change the travel date to sometime within the ticket validity period for a fee of 1000 AM or USD 25 (assuming you can do that online, and before the date of departure; otherwise, it is 4000 AM or USD 40).

If you don't cancel, there is no certainty that you will get the three empty seats though. The best chance of getting those seats is to check in your family members online and then inform the gate agents right before the gate closes that your family will no longer fly. In that scenario, you will likely lose the entire ticket (including the taxes and fees) but you will hopefully get a row of empty seats. This is assuming these are one-way award tickets, because if you no show for the outbound flight, the return segment will automatically be cancelled as mentioned earlier.