HI Mikey, DT is right about that caliper, don't even think about fixing it, just chuck it and go for a replacement as he suggests cos you will be chewing gravel or the back of someone's car if you ride with that thing.
PS just asking here but in your 2nd photo, close up, is that another crack/fracture just to the right of the rusty philip's screw? Someone has really done a number on the thing if it is, must have fitted it with a sledge and a cold chisel !!