Stevens's relationship with his son was terrible. He didn't show him much affection, never hugged him, always saying "I'm a little busy here, Paul." and got him a plastic chicken you hop around him rather than a Big Wheel like he wanted when Paul was 6.
He died at an unknown period from an unknown cause. This is evident as Paul says in The One With The Ring "I miss my dad.".
Mr. Stevens Sr. most likely had a good relationship with his wife.
As stated above, Stevens Sr.'s relationship with his son, Paul was a terrible one. He never showed him much affection and was apparently quite neglectful of him.
Nothing is known about his relationship with his daughter.
- The One With The Ring (First mentioned)