. . . are a great source of information, if you can find them.
Normally, the wills will list the name of wife/husband, children, and often grandchildren and in-laws. By finding the last wills and testaments of various ancestors I have been able to verify the siblings and children of my ancestors.
Normally, I just do a simple Google search, such as "last will and testament of philip edelen" and see what pops up. I've been pretty lucky so far, finding quite a few excerpts or complete wills for my ancestors.
So, when dancing with the ancestors, look for their last wills and testaments. The information contained in those documents are a great source of information.