Thanks for you suggestion! I had my family member contact customer service again and ask them specifically to check and see if his KTN number is in the reservation. He said he thought they had done that because he gave him all the information and they told him the reason he didn't get TSA precheck for his first flight was because his middle name wasn't on the reservation>
This time the customer service rep started out by saying he needed to have his middle name to match (lesson learned to double check when someone else is making reservation), make sure his KTN is in his Delta profile He told them he KTN number was there before the ticket was booked.
The customer service rep then said he can see that his return flight already has TSA pre-check attacked to his reservation. So she says it will show up on his boarding pass for the flight home. Fingers crossed!
Not sure why the previous reps couldn't see this, unless it just happened with the past couple of hours.
Thanks, again!