My fiance family has alot of dieases but my finance still wants to have children.?

It seems to me that most of those things are treatable and not completely debilitating diseases. The hyperreflexia is caused by spinal cord injuries and is not something that someone is born with (see sources). I wouldn't be too worried, but of course if you don't want to have kids, then you need to talk to your fiancee about this. Maybe discuss adoption?