I'm visiting Krakow at 19th-23rd of this Month with a group.

I've read multiple times that on the 20th and 21st of April 'everything is closed' for Easter.

If true, this equals that the only days that we can visit museums/castles/restaurants is at 19th and 22nd.
My group wants to visit Auschwitz Birkenau at 22nd. I prefer rather to visit museums than go to Auschwitz but it's probably the only chance I will get to visit it.

Should I go with my group or ditch them to see other stuff?