I was wonder can a PC become his Cohorts familiar example below
at 7th level I take "Leadership" to gain a witch familiar
at the witch's 5th level (probably my 7th), she takes "Improved Familiar" I become here familiar
at my 7th level/witch's 5th, I gain the ability to share spells, and store spells, and we have an empathic link, I can deliver touch spells (and hexes) that the witch casts and we follow the standard rules for this where I must be adjacent to her at the casting (not for hexes). Also, we gain the "Speak with Master", but that's kind of redundant other than no one else can understand the language.
at my 15th/witch's 13th the witch gains the ability to scry on me
This supersedes and replaces the normal familiar rules, and I gain no additional benefits from being a familiar. I don't see how this is overpowered. I have to use a feat (sort of), and the cohort has to use a feat. she gains no additional benefits from the feat and would have been a cohort regardless with me taking leadership. The features we gain aren't especially powerful since using me to deliver touch spells requires that both of us use our standard action to do so, taking me out of any other form of combat, and since I am the primary (not the cohort), that could be a big thing.