This could be the most difficult award to come by, and even more so due to the need for two seats. Concorde awards were easier to come by back in the day.

I know of only one person who secured two F award seats on Trans-Pac SQ service back in 2001 (pre-9/11) using DL miles. They got an award one way in F for both pax, then on the return, F for one and J for the other. They had to "pay" the F miles for the part F, part J ticket. DL said they couldn't waitlist the J pax for F (no "waitlist" concept exists for these tickets, supposedly). Pax called SQ, who did waitlist them, and the second F seat ultimately cleared at the airport.

This is the only time I've heard of someone booking two F award seats in advance on SQ (for the one segment where they were both in F).

You may want to try the book J but pay F approach. If you don't get the F upgrade, I suspect that it's unlikely you'll get the incremental miles back (but a letter to SQ would be worth a try).

Not to be picky, but if they get F, recommend the two seats together in Rows 3 or 4 of the F cabin on the 747-400s - those are really the only two sets that work for travelling couples in terms of being next to each other. The suggestion in row 2 doesn't really work.

I've been in SQ F twice - I've been on Concorde and flown privately a bunch, and once you're on board, SQ F was the finest flying experience I've ever had.