That's great advice about checking FamilySearch. I've now downloaded the 6 pages (images 61- 66 of 752) of the passenger list for the Mary Ann, which arrived 3 Oct 1851.
The images have been transcribed, but I can't find Eliza or Sarah in either the transcription or the actual images. https://www.familysearch.org/search/collection/1849782
What I have learned is that the images don't have much more than the transcription, so can't help with confirming if they are my family.
No luck with searching city directories so far either, but that may be because it's too early and they weren't had of a household.