I know you have probably already discovered this but the reason they are so tight is because the person doing the assembly got carried away with the thread locking fluid, like LocTite.

My only suggestion, and what worked for me, is t make sure you have a Phillips head screwdriver that fits perfectly. That way you stand a better chane of breaking at least one screw free. Of course, you then have to get the feathing shaft out of the bearings and that is another problem.

Once you do finally get them out, replace them with some 2x6mm hex head screws.

Carl