The closest terms that I found to be similar to "bemka" and "mamcu" were bunka and mamchu. The origin for bunka is Japanese and the origin for mamchu is Tungusic.
'Bemka' is a word of Russian origin, meaning "eggplant" in English. 'Mamcu' is a word of Esperanto origin, meaning "grandmother" in English.
No. There is no Hebrew name for Nancy, so it would be the same in Hebrew as it is in English: Nancy. It's spelled ננסיMamcu is not Hebrew.