Were my husband's ancestors possibly Jewish converts to Catholicism?

In trying to do a family tree on Ancestry.com, I found out my husband's two grandmothers' maiden names were Moscowitz and Kravitz. Those I always knew to be Jewish names, although his family practiced Catholicism as far back as he was aware (grandparents and parents). Are those primarily Jewish names? Were my husband's ancestors possibly Jewish converts to Catholicism? How can I find out? All of his parents and grandparents are deceased. All of his grandparents came from Poland in the late nineteenth and early twentieth centuries.

Pardon me, my husband's grandparents all emigrated from Poland to the United States in the late 1800s and early 1900s.

Yes, these surnames definitely look Jewish. MOSCOWITZ would be the English respelling of the Polish Mośkowicz (son of Mośko or Moses).
KRAVITZ is the Yiddish word for tailor, borrowed from the Polish krawiec.

For more information on namesakes in Poland and contact with a Jewish genealogical researcher please contact me.