Should be a good trip. Krakow is the closest to the Ukraine that you’ve mentioned. I went to Krakow via Prague after our 2018 Berlin reunion and it was enjoyable. Of course, visiting Auschwitz was serious.
In Prague, during the summer tourist season, the famous Rte. 22 streetcar is pretty crowded. It’ll be interesting to learn how things go in the winter with the pandemic.
-- rwr