Shelly,

You are not going out on a limb you are thinking like a scientist! We do think that while there are a lot of genes that are involved in the development of the CDH many of these genes are related - they interact with each other in development. For example there are two gene in the GATA family that have been identified to cause CDH. While they are two different genes, the proteins they make interact with each other and are both important in the development of the diaphragm.

With regards to your question about a connective tissue disorder. Yes I do think that a small proportion of individuals with a CDH have one because of a connective tissue disorder (your family and the others you listed might be examples). This is just one example of how diverse the genetic causes of CDH are.

All the best to your family!