Hope they aren't joined at the hip and you do get Dad time, sounds like you could possibly get Step Sisters help. Love the idea of recording your Dad, and doing the memory thing. My father always had great stories and funny little sayings like "so I said, let them keep the $50,000) Sadly, now he has dementia and those stories are lost. Even though he is still here physically, I lost him about 3 years ago and so wish I had done more Dad time.
Good Luck and just think someday maybe your kids will write for advice about you - tee hee, that is what I tell mine