Welcome! I'm Ron Z! I will do my best to answer all of your questions. For easy access to this thread, bookmark it now! Please read everything!
Looks like you may have two different problems here.
The P0420 is fairly straight forward pointing to a failing Catalytic Converter. The oxygen sensors measure the amount of emissions in the exhaust going into, and then out of then out of, the Converter. When they see the converter isn't "cleaning" the exhaust enough to meet specs, the converter is deemed" below threshold" and the P0420 is set. Most commonly, the converter will need to be replaced in the near future.
The P0441 is actually a "known problem" and Toyota has issued a Techincal Service Bulletin, with the correct repair for P0441:
Diagnostics for PO441:
Attachments are only available to registered users.
This being a known problem, is it covered by Toyota?