Complex sentence: All three DuMont-owned stations are still operating and coincidentally, all three are owned-and-operated stations of their respective networks, just as when they were part of DuMont.
Split into simpler sentences: All three DuMont-owned stations are still operating, though they are now affiliated with other networks. Coincidentally, all three are owned-and-operated stations of their respective networks, just as when they were part of DuMont.