I'm taking a family trip to Asia in August, and I'm trying to figure out how to best book what my parents want using miles. They want to fly DEN-HKG and SIN-DEN in J. They want to connect in SFO in both directions so I can meet up with them and be on the same flight. Their dates are pretty firm.

DEN-HKG has IN availability and is therefore 85,000 miles per person. Great.
SIN-DEN, if booked as a multi-city with the outbound, is 255,000 miles per person on the AM departure with Polaris 2.0. Steep price, yes, but that's the flight they want.

They have enough miles between the two of them – my dad has 527,000 miles, while mom has 210,000. But they don't have enough in one account. So I decide to try booking them as two one-ways: DEN-HKG using mom's miles, and SIN-DEN using dad's. But the one-way SIN-DEN price hiked up to 384,000 miles for the AM SIN-SFO departure. The PM departure remained at 255k. As we were looking at this for 20-30 minutes, the AM departure as a one-way then hiked up to 406k. I don't know if that's the algorithm getting nutty with me looking at it so much, but it's just so frustrating.

Is there anything I can do? It seems like trying to transfer mom's miles to dad's account would be prohibitively expensive. I'm not sure if miles pooling is the answer, as it seems like there's such a delay with every move in that method. Plus, I'm not sure if this itinerary is eligible to use pooled miles, is that right?

Anybody have any other insight on why this is happening or another solution? I knew cash tickets price differently as one ways versus roundtrips, but I didn't think that was ever the case for award tickets.