Of course nothing can be ruled out per se, given the quality of these photographs, but I would disagree that the possibility of the aircraft being single-engined should be given the same weight as it being dual-engined. The bifurcated contrails are seen with all four airframes, not just one, and the distinct gap between the contrails suggest that they are indeed bifurcated rather than it being due to image distortion brought about by the low resolution. We all agree that better cameras would yield more definitive answers, but we need to work with what we have here.
Well, I also agree that the possibility of the aircraft being single engined should not be given the same weight as it being dual engined -- I think the possibility of it being single engined should be given more weight than it being dual engined.
Even in the video, it looks as much plausibly to be a single contrail that is dissipating as it trails the aircraft, rather than two separate contrails dissipating over distance.
We have examples of twin-engined UAVs that are much smaller than the J-10 or the various UADFS.
Sky Wing III (prototype precursor of the WZ-10):
View attachment 169321
WZ-10:
View attachment 169322
CH-805 target drone:
View attachment 169323
Star Glory SG-1 target drone concept:
View attachment 169324
The rapid pace at which the objects appear to be moving relative to the clouds kind of suggests that these are smaller aircraft rather than a platform in the size category of J-10 or even GJ-11.
Another clue is the supposed location - northwestern China - which kind of shifts the probability of these aircraft in favor of them being UAVs rather than manned platforms (Malan Airbase).
I am aware of those UAV examples, and they are exactly what I had in mind as causing me to be more intuitively cautious of twin engine setups, because they either have been procured only in limited numbers, or not procured at all.
It would be a bit of a step backwards for a tactical or smaller UAV to be twin engined, especially if it were J-10 sized or smaller. If they were Flanker sized or larger otoh, then it would actually be more plausible for a twin engine UAV to make sense.
Which circles back to the "not impossible, but should have relatively high threshold to suspect," for a tactical sized or smaller UAV to be twin engine rather than dual.
