Family Ties/WMG

What happened to Elise's brother Uncle Ned?
Uncle Ned, played by Tom Hanks, was last seen in a second season episode. Ned becomes an alcoholic and the last time we see him he's on the phone calling A.A. It's possible that Ned drove to the meeting and wrecked his car, killing himself.
 * Or he fell off the wagon and the Keatons told him not to come around the house anymore.

Marty McFly is Alex Keaton's twin brother, and they were separated at birth
Let's say the Keatons had twin boys, but they were so broke they knew they could only manage one at that time. They put the other up for adoption. Then their subconscious disdain about their finances is deeply driven into Alex's subconscious. Marty was adopted by the McFly family.
 * Or else, they're identical cousins -- and Elyse Keaton is George McFly's younger sister. After their biological father died, their mother remarried.
 * Michael Flaherty is also their cousin, and Michael's mother and Elyse are twins. However, Michael's mother was adopted - as their parents could not take care of both of them. As such, Michael and Alex don't meet - until Michael moves to Ohio in 2000.