I am not sure if I would go to Zakopane just for the day as in normal conditions it's between 2 and 2 a half hours drive each way, so 4 to 5 hours of driving just to get there and back, giving you limited time there. However due to traffic it can take a lot longer than that, it took me 3 hours to get there by car (with a local driving, who knew the back roads and best ways to avoid traffic) and over 4 hours to get back by bus (cost 20 zloty or about £4) due to heavy traffic.
There is a good overview of Zakopane here: www.adventurous-travels.com/posts/zakopane-what-to-see-in-polands-winter-capital
The Salt Mine you can visit with a wheelchair which uses a route with a lift and visits the main parts/highlights like the 'cathedral' but you need to book in advance, as there are only a couple of time slots available each day.
Aushwitz, the tour companies are all basically taxi services as it's Aushwitz tour guides who do the tours of both camps. But although a lot more expensive than taking the bus, it does make it easier as they pick you up at your accommodation, tickets and tour time are sorted for you, they ferry you between the 2 camps (although there is a free shuttle bus) and then take you back. So mostly, they just wait around for you all day and act as a taxi service.
Be aware that some parts would be difficult or impossible with a wheelchair as in Aushwitz 1 the exhibits are mostly inside buildings, with entrance and sometimes internal steps and narrow corridors (divided into two to allow tour groups to pass each other single file in different directions). The external paths are also quite rough gravel etc and in Birkeneau there is quite a lot of walking.
Krakow itself is easy as the Old Town is largely pedestrianised, flat and there are horse carriages and electric buggies everywhere. The castle has a steep entrance though.