What’s with all these washers?

Yup they are threaded. Soak them down good with Sea Foam Deep Creep for a few days then try to get them out. They do look like hell.
Agree, the heater hose nipples are threaded. Soak them inside and out with penetrating oil for days, and with persuasion they will thread out. Usually it takes a small pipe wrench and you will crush them during the removal process. Dorman has replacements.