I read the second half of the passage like so:
utrum omnes quasi occiderint teneantur videamus
videamus, utrum omnes teneantur quasi [servum] occiderint
"let us see, whether everyone should be held as if they killed the slave"
"we will consider whether everyone is liable for killing him"
This is somewhere between the two translations you quote.
The word utrum strongly suggests that there is an indirect question.
The way I parsed it, the main structure is:
videamus, utrum omnes teneantur
"let us see whether everyone is held"
Then this teneantur is further explained with quasi and occiderint.
You could say that occiderint is subordinate to teneantur which is subordinate to videamus.
The rules of consecutio temporum for subordinate conjunctives are followed:
The present videamus is not subordinate, but more of an optative "let us see".
The verb tenere is subordinate to a present thing (videamus) and is contemporary to it, so present conjunctive is just the right thing.
The verb occidere is then subordinate to it (or videamus; it doesn't matter which way you see it) but prior, so perfect conjunctive is correct.
The first quoted translation appears to be mistaken.
It says that we consider everyone to be liable, whereas the original says that we consider whether everyone is liable.
It turns an indirect question to a statement — an unknown matter to a known one.
The original text does not comment whether they are all liable, just that it should be looked into.
The second quoted translation cuts a corner short.
It replaces "let us see whether they are liable" with "are they liable?", and this simplification makes sense to me.
I would consider this reasonable streamlining, but it depends on the surrounding context.