This is not making sense. You got the radiator replaced because the engine was shaking? Is there a paragraph or two missing there somewhere? After the radiator was replaced, the car still won’t start, another paragraph missing? The fuel pressure drops off and they found antifreeze in the cylinders, two or three paragraphs missing?
None of these things are related with the exception that if the fuel pressure is dropping off after turning off the key and the engine not always starting. That would indicate a leaking injector that is flooding the engine making it hard to start. It might also make it run rough but should set a code.