IMO you are making life harder for yourself than it needs to be by using MDI and Child Forms.
If your application is the 'standard' genealogy type then it is very similar to a UML, Class Diagram or Organization Chart application, just the information contained in the 'boxes' will be different.
Might I suggest that you search for Open Source versions of any of that type of program. e.g. StarUML
] (there are loads more out there).
Have a look at a few to see how they do it and pick the bits that make the most sense to you.