Which of the optical sensors in operation on the three spacecraft currently en route to Mars (China's Tianwen-1, UAE's Emirates Mars Mission (Hope), USA's Mars 2020 (Perseverance)) could image one of the other spacecraft, with resolution more than one pixel, assuming a correctly aimed sensor or spacecraft?
I couldn't find technical details of Tianwen-1's (orbiter's?) optical navigation sensor.
The Hope orbiter's EXI imager has an angular resolution of 22 arc seconds, but it might be turned off during cruise.
The Perseverance rover is inside an aeroshell. Photos from Lockheed Martin show that it has at least one small circular window. I couldn't find details of optical instruments outside Perseverance, nor whether an interior instrument is aimed at such a window.
So it might come down to Tianwen-1's sensor's angular resolution and how densely packed this convoy ever becomes.