AvWeek's coverage of the Ukraine crash was surprisingly sparse. The aircraft was a Su-27UB, a late model two place trainer version. This explains why everyone kept saying "both pilots", although it doesn't explain why two people were flying in an airshow hop. According to the report, the pilots ejected before the initial impact, even though when I watched the video it certainly seemed that the canopy was intact when the plane hit the ground. Again according to the report the plane first hit some trees, then whacked the nose off an Il-76 transport, then tumbled into the crowd.

Also found this interesting report, which implies a possible bird strike.