This UFO must be huge, because the space station itself is 109 meters across and 73 metres wide, and in comparison with the space station and the distance we can assume the smaller of the UFOs is about 5-10 metres and the longer UFO is about 20-25 meters. 

Also note in the video that the astronaut asks about the interval between teh photos taken from the live cam on the ISS, as he hints at the UFO being there without actually saying so.