In one family that I know of, there is a third cousin, a second cousin, a cousin, and a parent who are either gay or bisexual. And none of these people are closely connected... they may have seen each other once every seven years or so at family gatherings.
I don't know what explains the high numbers in this group. And conversely I do know of other families where there are no gay family members.
I think all statistics should be set aside for now, because nothing seems to be conclusive.
My guess is that an even larger percentage know someone who is an alcoholic. The difference is that the alcoholic goes to AA to try to stay straight.
73.4% of all statistics are made up on the spot.