Split at York and Hartlepool.
Oh, and the cheapest valid ticket from Sheffield to York if travelling off peak returning same day is from Shireoaks (The shortest route is via Sheffield and Thetrainline is happy to book you that way).
I recommend sampling Grand Central if you can get the 1114 off York (if that's not too early) or the 1730 from Sunderland (if that's not too late).