متن اصلی - لاتین - Quod ordines seu sectiones librorum Sacrae...

Quatuor ----> quattuor.

Seing that "sint" is in the subjunctive, is it possible that the meaning is slightly different: that the orders of scripture ought to be four?

If it is only a clause - it cannot be rather translated in other way, but if it is a separate, independent sentence - yes, it can be translated:

Because the division or sections of the books of the Holy Scripture ought to be four...

but I think we need a larger context to be sure of it....