Been there, done that. Here are attached two frames from the gun-camera movie. The He 177, the two SM-82s and the SM 81 are visible, as well as the twin-boom aircraft:
This is a closer frame...
The S.82s were used in vast numbers by the Germans, so their presence is no surprise. The twin-boom a/c is in very bad conditions (an eventual dark green top camouflage looks completely ruined and/or washed down).
The grain of the film is too coarse and the frames too fuzzy to attempt an identification, although the machine could even be a Gotha Go 242 glider with the front fuselage burnt down (which would also help to explain the tail-heavy attitude...).
Concerning the thoughts about the SM.91 (which could apply also to the SM.92, BTW) both prototypes of the two aircraft were destroyed in an Allied bombardment on Vergiate on 27 December 1944.
The airfield in the images however definitely isn't Vergiate and no He 177 was ever located there (there are extracts of the airfield's log to prove that).
So the ID of the unusual aircraft is still unknown...