Like many celebs and public figures it's pretty clear that Bill and Melinda Gates were both replaced by doubles. This occurred in 2013.
It's also pretty obvious that the replacements are both inverts. Bill and Melinda Mk2 are both trannies. Again this is fairly standard practice.
But where it gets weird is that a lot of people are now wondering if Melinda is being played by Kevin Kline? Personally I'm not attached to this theory, but at least more people are starting to ask questions...