I have an option of booking my dad on 100k of my skymiles Economy TPA->ATL->JNB and back OR for 120K with the only the outbound TPA->ATL on First and the remaining three legs on Economy.

He has an additional Gold Delta Amex which i don't think allows for a free second checked without me (the base) flying. Can the 2 bag allowance on the 120k 1st leg be used to check 2 bags all the way through JNB, do I have to pay the difference for ATL->JNB or do I have to recheck and then pay for the 2nd bag in ATL.

All flights are on Delta. I realize, regardless, we will be paying for an additional bag on the return trip since all legs are economy.

Thank you in advance.

Any other tips are appreciated.