Crossbows were “banned” for use against Christians just like today underage drinking and running red lights is forbidden. Nobody really seemed to care about it and after 60 or so years the rule was changed so that it was allowed to be used against Christians if the war against them is just. Notice how “just” is rather open to interpretation. The whole gist of the law was that Christians really shouldn’t be killing each other at all which is what happened during the 12th century. You had all these little family feuds or little wars involving 50 folks or less. Kinda like the Godfather 1150 AD.
That said the poundage of the bow is most likely very light and it would not hurt anyone wearing any kind of protection. The tactic looks fine if your shooting with another 300 guys behind your back and just trying to hit unarmored parts/horses.