Have a great trip with your family. We also live in Eastern Washington and often fly from Spokane (GEG) or Pasco (PSC). We also make the drive to Seattle (SEA) from time to time when the airfares justify the cost of the drive and parking.
Our family is older than yours, as the last of our four children is just leaving home. We have greatly enjoyed traveling with our children over the years. When the children were younger there were trips within the United States and cruises. When they were teenagers we started doing international travel.
Because there were six of us, pricing was almost always the most important consideration. We found that when flying to South America or Australia, we could save $400-$600 per ticket by getting to Los Angeles (LAX) to begin our international trip. (Round trip Spokane to LAX usually cost us around $200 per person.) We also used Vancouver (YVR) to get to London (LHR) when the price savings justified the drive.
I am 6’3” and my wife is 5’4”. When flying as a family we fly in the economy cabin. (Somehow when you are all related the seating does not feel as cramped.) When flying just as a couple, we will pay for the extra leg-room seats. I also have status on Delta, which allows me to select exit row seats at the time of booking.
Enjoy traveling with your family. We have such wonderful memories of traveling with ours.