Help please!!! Screw won’t loosen

The screws are likely rusted in place.

Drill the head completely off so you can remove the aluminum parts. Then try the following:

• generous application of penetrating oil, followed by a 24 hour wait. Put vise grips on the shaft (pliers will not work) and use a hammer on the vise grips. You want a sudden movement here, not a steady turn

• heat the part and then use the vise grips again. And by "heat" I mean glowing dull-red. Grab it with vise grips while still glowing.

• the above may simply twist off the shaft, but that's step 3 anyway. Grind it flush with the rest of the metal, heat it up bright red, preferably orange, and let it cool completely. Do NOT quench - heating softens the metal, rapid cooling hardens it. Drill and tap a new hole. If there's too much corrosion in there, drill a bigger hole. If it's really nasty corrosion, go all the way through and use a bolt, and if it's bad enough that the bolt won't work, get a new grill.

I'd drill the existing screw head off, use a bit slightly larger than the shaft of the screw but smaller than the hole in the knob. The stripped out screw should keep the bit fairly centered even when used at a slight angle. Once each head is removed you can pull the knob and try a screw extractor on what's left, but there's a good chance you'll need to replace the entire lockset at this point.