Hi Marlespo,
Hope the big move has gone ok for you. I just saw this post and thought I'd throw this out there -- you can look-up the family on Ancestry.com. Not sure of the age-group we're talking for your grandmother-in-law and her brother, but I'm thinking they would be listed in at least the 1930 Census, if not 1920 and 1910. You can find out some basic info that way.
To find out if her brother is still alive, you can try looking him up on the Social Security Death Index, which I believe is free on Ancestry.com.
If you can't access any of the info on Ancestry or even Genealogy.com, you can feel free to let me know and I'd be happy to look it up for you, as I have a full subscription to both websites.
Good luck,
Jeannie