I am dealing with a rather frustrating issue, wondering if others have experienced this before.. would greatly appreciate if you can share any insights~

basically I found a one way trip redemption availability for 2 people in J (this availability is an exclusive availability only for DMs - ones with a black star), but I am unable to find award availability for the outbound leg. Upon checking, I see that the one way flight from HK to Japan is actually similar price as a round trip return leg. As such, I book the round trip leg and hoping to use miles to "upgrade" the return flight only. However, upon trying to speak with a representative twice via whatsapp and trying the online route, I cant upgrade the return flight leg. The return leg is not selectable for upgrade (i have booked an upgradeable ticket), and the whatsapp rep is also hopeless where he/she is unable to see the award availability given these are only seen by selected members...

so I am contemplating now if i should just redeem the return leg in J and keep the overall ticket. However, im concerned that there might be issues with checking in since I will basically be double booking the same 2 passengers on the same flight with separate seats... is this an issue that i should be worried about or this is fine?