Translation:The women eat a sandwich and they drink milk.
Use of singular implies one sandwich per person. In a more general context if each person has or can have only one of an item the singular is always used. For example "their heads" in English goes into Irish as "a gceann" (their head) - "a gcinn" (their heads) would sound most strange as it would that they had more than one each. The sentence as it stands is correct.
In both Ulster Irish and Connacht Irish, certain worlds that are spelled with an "n" have an "r" pronunciation. (cnoc is another example that crops up on Duolingo). In Munster Irish, and for most people who aren't native speakers from Connacht or Ulster, the "n" is pronounced as an "n".