They're talking about various rumors that Heinlein had an unconventional sexual lifestyle, as did characters in many of his books.

I personally hadn't heard of any of those rumors being proven as fact, but there were always lots of people who took them at face value anyway.

Another mystery (to me) is that I could've sworn that Heinlein had at least one child, but last time I checked, I couldn't see any trace of that on the web, not even rumors. Maybe I just have a faulty memory about that.