So about the armed guards, I didn't think it was possible because armed troops were prohibited in Rome, but what chōrs is referring to here must surely be cohors urbāna, the Roman paramilitary police force (though boyscouts by American standards) established by Augustus as the gang to end all gangs. The corde-emendation seems wrong.
Lēgēs referring to the Twelve Tablets is actually a very elegant solution to the problem of joining it with cernere "to make out, catch sight of", a physical action which would sound very awkward with some abstract laws as the object. However - and I didn't end up explicitly saying it - it still (or is it again?) seems to me that cernere belongs to tribūnal alone, while the elided verb in the previous clause is the videt from the preceeding coordinated sentence. This is simply because the supposed ellipsis of the left verb would violate the rightwards linearity of language: I like apples and I like oranges => I like apples andI like oranges but I like apples and I like oranges . I think the syntax here is as in the English translation: 'Those who destroy cities see wars and bloodshed, while those who plead cases see the forum with its Twelve Tables, and tremble at the sight of the Bench surrounded by guards.'
Lēgēs referring to the Twelve Tablets is actually a very elegant solution to the problem of joining it with cernere "to make out, catch sight of", a physical action which would sound very awkward with some abstract laws as the object. However - and I didn't end up explicitly saying it - it still (or is it again?) seems to me that cernere belongs to tribūnal alone, while the elided verb in the previous clause is the videt from the preceeding coordinated sentence. This is simply because the supposed ellipsis of the left verb would violate the rightwards linearity of language: I like apples and I like oranges => I like apples and