Traveling from Tokyo to Otaru

Hi Daniel
We are a family of 2 adults and 3 children aged 1, 6 and 8. We are travelling to Japan on the 12 of December 2023 until the 27 of December.

The itinerary is:
Arriving to Osaka 12dec
Leaving Osaka to Tokyo 15dec

Tokyo from 15dec to 20dec

Leaving Tokyo 20 dec to Otaru

Otaru from 20dec to 27dec (car rental)

27th back to Australia

We want to get the Jrpass for the longer trips so we were thinking on getting the 7 days pass activate it on the 14th so we can use it for travelling on the 20th from Tokyo to Otaru. Would that be ok?
We are struggling to find the times that the train to North Island leaves. We need to be in Otaru at 6 pm at the latest to pick up a car.. At what time do we need to leave? Where I can find all the departing times and trains that we need to take. What would you recommend if we are travelling with kids.
We checked Hypedia but don’t understand much how to use it or the different times the train leaves as well as arrival times.
Thank you
Madhya