TooT may or may not work, depending on how different the video is. It doesn't actually average the sources together, but rather compares all three sources and outputs the information that's consistent in at least two out of three sources. So like if there was a rot spot on one of the captures, it would take the information for that area from the two sources that don't have the rot spot. If all three sources differ, then I think it defaults to the first one.

The other avisynth filter you might try is Merge, which actually does average the two sources together.