Seriously doubtful for either of them. The 5k/10k doubles are far from what you want to be doing prior to running a good marathon. Of course, they weren’t training for the marathon at those points either and had never run one.
Wanjiru’s 2008 Olympic marathon was considered by many to be the greatest marathon ever run. This was before super shoes (and possibly other factors) and 2:06 was a much faster time then, and it was hot and humid during the race which made 2:06 seem inconceivable. I think even prime Bekele most likely DNFs when he gets into the heat of that one.
Mo Farah fully rested after a good marathon buildup doesn’t win the 2012 race 8-9 times out of 10. It was warm and sunny, pre super-shoes and with a slow start, so the 2:08:01 winning time is deceptively strong. Kiprotich beat Abel Kirui and Wilson Kipsang, who were both locks for top-5 in the world at that point (Kipsang considered by most #1, having already run 2:03 and won London). After completing the 5k/10k double, Farah may have been able to finish top 10, a few minutes behind Kiprotich, but it would have been an exceedingly painful experience.