I can't find the answer to either of these questions on the internet. Surely someone as paranoid as Joseph Stalin would think twice before keeping the husband of someone convicted of treason in a top government position? There must be more to this story!
There is no evidence Stalin was paranoid which is a hereditary mental illness.
However, Polina Zhemchuzina as one of the most powerful woman of the USSR openly supported in making Crimea a Jewish republic. That's seems to be the main reason Stalin not only imprisoned her but also criticized her husband. Stalin thought Molotov was the henpecked husband influenced by his mentally-stronger wife.
So perhaps he "removed" her to keep Molotov loyal at his side?