brace the bike ahead of time against a bench or wall. find the absolute fattest screwdriver blade you can get in the slot. tap only enough to keep the blade in the slot. give it all you got, they do bust loose.
I just noticed your bike is a Huffy. Huffy's are good bikes & make great looking motored bikes. I am going off topic only for this important issue. Huffy front fenders are famous for breaking loose & causing crashes.
This is a fact. Do NOT ride your bike with this fender.
The old hammer type impact driver is the best way to get those screws out. If you know someone who works on old cars or motorcycles (especially asian ones), he no doubt will have an impact driver. Otherwise, like everyone else said, keep tapping the heads of the screws using a large blade screwdriver and eventually they should loosen up enough to to get them out.
Why would you want to get inside the clutch? The problem seems to be your woodruff key on the crank to engine sprocket. What is inside the clutch that you would want to get to? The clutch is on the right side of the motor. You can remove your dust cover side plate to inspect the clutch hub, plate, pads ect... What I would like to see is video of your engine sprocket will you are moving the bike forward and backward. That is what I would like to see.