Yeah, it could be cool if there were some place to find some less popular characters. Maybe they could do a rotation. There are so many possible rare characters that it's hard to even wrap your mind around. For example, we once met Launchpad from Duck Tales at AK. Who would have thought he was ever in the parks?
The last time we saw Timon was on our honeymoon in Janurary 2010. Not 100% sure where we are in this picture, though. I would recommend looking by the entrance to AK. There used to be a spot at Camp Minnie Mickey where you could often find rare ones, but I don't know what that's like now with Avatar Land.
For the step sisters and mother, we found them during the Christmas Party in MK in November 2010. Not sure if they still come to the Christmas party but you can check if you happen to be in the parks during a holiday.