@bumplbea - I wonder if it would help to cable those two trunks together? I will tell my son to call someone. There were ants and some debris in that crook, so I agree it is a weak spot. We took care of the ants and debris, and have been checking it monthly to make sure they do not return, but yes, we should have an arborist look at it - thanks.
@PacificPonds - my son has a newborn and is already planning a tree house. A swing would be nice to - maybe I will get my grandson one of those baby swings!