I don't think one could just say "protestant" as many of the faiths that you could put in that category interpret many passages differently. Very differently in some of those cases.
Usually this claim that it is impossible to settle on a bible (using the Catholic version if a school district chooses) is brought up by liberals trying to fight Christianity.
Now hold on just a minute there, pal. Who you callin' "liberal?" ;o)
Protestants use the King James bible, how complex do you think that a generalized school lesson is?
I imagine that the lessons could use the Catholic version or the Protestant version and teach everything that they need to for the course.
You are striving to blow smoke and try to turn this into something complicated that suddenly is beyond human abilities to handle, I don’t think it is and it seems that Texas doesn’t either.