Sharon, You came to the right person, I can get you started.First do a RootsWeb or ancestory.com search or any search for John Jacob Obermayer or John George Obermayer.This is the first spelling you will find and the first 2 brothers that came to American on the ship 'Brothers or The Brothers'.
I am descended from both as my gg-grandparents were both Overmyers and descended from both sides of the family.Sarah and Jacob Overmyer.Now the spelling makes no difference here as many spelled it different ways, but these are the spellings they are listed online.
Ed Tokarz is one that has a great website and all information you could want.
Do you know the date of your Mary?I can't seem to locate my info at the moment, but think she may be the sister to my Grandmother, May who married a Goetzinger/Getzinger.Ever heard that name?
Also many were sisters in Grandma's family and there were only one or 2 brothers.Some of her siblings were still living when my grandmother died, we just never met them as my folks knew others didn't like being bombarded with so many of us.
I am in contact with another cousin who's grandmother was Sarah, another sister of my Grandmother.
My g-grandparents raised their family in Monroe, Monroe Co, MI and many are still there.
There is also information for Fort Overmyer/Obermayer in PA where our ancesters were well know and soldiers.Len Overmyer on this forum has plenty of information too and is a cousin.Should your Mary be the sister of which I am thinking and the child of Clarence Overmyer, I have a picture of her and the whole family shared by another cousin on here.
I am lucky enough to be related to all of them due to the marriage of 2 descendants from each original brother that came over.
If you can't find the site, let me know and I will find it again to help you out.