I’ve never did the Camino Português, so I don’t know about hostels and albergues. But I lived in Lisbon for 5 years and I know from personal experience finding something open on Christmas Day was always a challenge. Christmas is a big deal for the Portuguese and it’s considered a family day. I believe hotels and hostels will be open of course, but on Christmas Day most shops and restaurants will be closed, except for the ones that are offering special menus (in which case I recommend booking early - two weeks before may be not enough time). Even grocery stores are closed, although some open only for a short period in the morning, and Taxis may be difficult to find.
My advice would be booking ahead all you can on the actual festive days just to be safe.
If you need help with Portuguese translation to make bookings feel free to send me a message, I’ll be happy to help.