New Marks Found - How is Fanny Related?

I have been in touch over the last 24 hours with a gentleman from Santa Cruz, California. He is the great great grandson of Fanny Marks.  How is she related?  We suspect strongly that she is, but do not know exactly.

Here's the story:

My great great grandfather Louis Marks had a brother Emil Marks.  They were naturalized on the same day in 1864 in San Francisco and died 3 months apart - Louis in December, 1888, and Emil in a train accident in March, 1889.  While researching Emil, I found him in the 1880 census living with a widow, Fanny Lust and her children.  Fanny had been married to Simon Lust, who had died before the 1880 census.  Emil was listed in that census as a Lodger.  Now Emil was found in the 1860 census in San Francisco as a lodger and employed as a cap maker..  Next to him in that census was Simon Lust, also a cap maker.

There is a newspaper article in The Daily Alta California newspaper dated April 17, 1889, published shortly after his death that states that a Fanny Lusk (sp) was attempting to administer Emil's estate, so one would assume that they were related in some way.

Benjamin Lust was one of Fanny Lust's sons. In his mortuary record, it states that his mother's maiden name was "Marks".  Also, one of Fanny's daughters - Carrie, has her mother's maiden name identified as "Marks" in the California Death Index.

So with this evidence, it appears that Fanny and Emil (and Louis) were brothers and sister.  But then again, they just might be cousins.

The search continues!