I’m sorry to hear of all the problems your family have, I know it’s a constant worry, especially when you’re not getting answers.
Regarding the ‘inheritance’ issue you raise, I can only relate my experience, in that, my mother could touch her thumbs onto her arms, she also had a heart murmur and flat feet BUT she was never diagnosed with EDS. I had none of those features and have lived most of my life in a very active fashion and had no idea I had EDS until a head and neck injury triggered a boat load of symptoms (more like a war-ship than a boat!) nearly 10 years ago.
Since being diagnosed myself, I have been looking at the various health problems that my children (and grand-children) have had and I believe that most of them have undiagnosed EDS. Their issues are nowhere near as extensive as your family’s issues are but I share your concern. I thoroughly understand how EDS can remain undiagnosed, as the doctor will just treat that particular symptom you present with at the time, no-one really bothers about over bendy fingers etc, until they start getting pain in them. I think Dr D’s Theory, that EDS is grossly undiagnosed, is more than likely to be absolutely correct. So your relatives may have had it, unknowingly.
Incidentally, strange you mention hip issues at birth because my own youngest daughter had ‘asymmetric creases’ which the health visitor said may need to be investigated, as she may need a brace, luckily she didn’t, my older daughter’s hip easily dislocates too. My son has had fatigue issues since he caught pneumonia aged 4, he also never got 2 of his teeth, they just never arrived. My grandchildren seem to have issues which all could be related to EDS, vision, memory, bladder, swallowing, hypermobility, one grandson has quite a few developmental issues (speech, attention, co-ordination, etc) and a growth issue, which are currently being investigated.
I believe help is on it’s way, now Dr D’s on the case!