Tokyo to Karumai area with daytrips, back to Tokyo

My daughter (23) and I will be traveling to Japan on July 25. We will stay in Tokyo for the weekend and then travel North to see my son in Karumai, Iwate. I know they don't have a train station there- I think the closest is Ninohe, we will be visiting him and doing day or overnight trips in the north and then head back South to Tokyo after 7 days to leave from Narita on August 4- are there enough trains we can go on to make this a good deal? We would purchase the 7 day pass, but activate it when we Tokyo on Monday so we wouldn't use it from Narita into Tokyo the first day.