The basic question - are there certain flights HKG-SIN that are more likely to get 2 F award seats?

I have a BD award booking for two in November, including HKG-SIN in F. A TG cancellation and a rethinking of plans means we are no longer going via BKK, and I am trying to rebook direct on SQ.

I rebooked one seat onto SQ865 at the weekend, but unfortunately the hoped-for second F seat hasn't been released yet. I'm looking for advice on which of these options would be better:

- Book C on SQ865, and hope for another F seat to appear at some point, leaving us at least both on the same plane.

- Book F on another flight, eg SQ863, and hope that another F seat appears on one of the flights, but risk everything disappearing and ending up on different flights altogether!

I wondered if maybe the later flight was more popular (although it is a Saturday) so was less likely to get a second F seat? I know one might pop up much closer to the time, but if I could get two confirmed sooner rather than later then I might get less grief from the other half!