The link you provided suggests that one of the main ways for carbon to enter the atmosphere or ocean is through volcanic eruptions and geological hot spots. Is

The link you provided suggests that one of the main ways for carbon to enter the atmosphere or ocean is through volcanic eruptions and geological hot spots. Isn't increased geological activity one of the results of orbital resonance? If the 'central' planet has 6 close neighbours of equivalent size in resonant orbits would this not provide a very large amount of 'stirring'? These planets are also much more massive than Europa which is only 0.008 times the mass of the Earth compared to ~.6 and ~1.3 Earth masses for the ones in the habitable zone. They may have a more substantial mantle and core, possibly global magnetic fields and definitely more gravity to hold on to any fugitive gasses. Considering geological timescales, this system is also billions of years younger than our own, potentially only a little over 500 million years old. The processes you draw concern to may simply not have had time to play out yet. I'm also not convinced that the atmosphere would be cold enough to freeze out gasses on the night side if there were significant oceans or enough atmospheric circulation to transfer heat from the day side.