Sandra, a few developments, I thought you ought to be informed as you've helped me so much.
I've found a document dated 9th May 1854, wherein Rosa de Ares, widowed wife of Benito de Ben, makes a declaration before the notary of the village of Puerto del Son (province of La Coruña, NW Spain). Incidentally, the notary is her late husband's nephew.
In the document, she declares that she is living with her spinster daughter, Rosa de Ben Ares, and that she used to live with her son Juan, who has lately married. She also says that the son she's living with now, Francisco, had emigrated abroad in early 1841 with his cousin Jose de Ben (presumably Jose Ventura de Ben, mentioned in the 1850 US census), with whom Francisco had lived and worked, and that Francisco returned home in July 1853 (the year before the document was written). There's no mention of what happened to Jose after 1850, nor who the third person mentioned in the 1850 census is, Manuel. I'm going to the archives soon, perhaps I'll find more information there. She mentions she is living thanks to the money her husband made in New Orleans.
Anyway, that fills in a few blank gaps, but still there are some questions to be answered.
Best regards!