I prefer to use the generic form for a source. I would use something like:
Setup New source:
Name: Smith Family Manuscript - Unpublished
Author: Jane Smith
Date: 1998
Source Citation:
Citation Detail: Pg 2
____________________
If something is not published, I prefer to call it a manuscript. A book implies (to me) that it was published and distributed publicly.
You don't mention how many pages it is. I would consider scanning the manuscript and attaching it as media to the source citations. If it's only five pages, I would add all five pages to one source citation and Paste-Link to all facts to be cited. If it's a lot longer than five pages, then maybe a source citation for each page. (Paste Link citation for each page and Paste Duplicate for each new page, then replace the specific page being cited.).