Genuine GM, AC Delco or Delphi sensors. I would do all 4 at same time. Typically not hard but if live where salt on roads, your rust may impede your success. Lots of penetrant will be needed.
Why do you think the codes accumulated over a long period of time? have you had CEL on and just ignored? Right now, you are guessing and that is exactly what the codes are for, to keep from guessing. Unless of course you have been ignoring the CEL.
By the way, when it comes to repairs and maintenance, lazy costs money. See my signature.