My family has a branch with very similar features to what you're facing. Tall, thin, hypermobility, flat feet, scoliosis. I was checked for Marfan as a teen and, just recently, an orthopedist wanted my oldest son screened. After speaking with a specialist, he said there was no way that what my family has is Marfan because we live too long. Marfan's patients rarely make it past age 50 without medical intervention. He didn't have an answer for what we have but he did rule out Marfan. You mentioned that your family are long lived so maybe you can worry less about Marfan.