I believe Saul made that up to cheer up Walt.They actually mentioned his previous marriages on "BB".
When Walt was wilding out about Skyler cheating Saul said something like "you think that's bad, my 2nd wife cheated on me with my step dad."
Fred.
Besides, Jimmy's mom is dead so there is no way for him to gain a stepdad anyway.
" to Saul about the bail money I was dying 



at Kim's bum ass mom.

It was dope when in the Hallway when Saul was spying on the family that an reflection of his face was shown on the wall 
