Some things to consider: a roundtrip out of Seattle is a closed-loop cruise which relaxes the proof-

Hello, I'm new to this forum and am planning an Alaskan cruise. I see some posts regarding this, but am still confused about the difference between north-bound, south-bound, round trip, and these 'inside passages'. What is the difference and what are the considerations that should drive my decision on which route to take?
Also, i'll have a wide range of ages on this family tour -- my mom will be 80, my sis and I are in our 40s, and I have a 7-year old niece. What cruise lines would you recommend, that might have activities onboard that could serve all our interests?
Inside Passage: The area of the long thin peninsula of Alaska that runs along the coast, when are airline tickets cheapest separating Canada from the ocean in many places. It is the closest part of Alaska to the 'main' United States. Some say it isn't 'really' Alaska since it isn't in the mainland of Alaska, but I disagree. It is a stunningly beautiful and peaceful when are airline tickets cheapest area.
Some things to consider: a roundtrip out of Seattle is a closed-loop cruise which relaxes the proof-of-citizenship requirements. A certified when are airline tickets cheapest birth certificate and photo ID will suffice. Doing a north or south bound is a one-way voyage, and even if it starts in Seattle and ends in Anchorage, U.S. law requires the guests to have a passport or passport card. This is because you have to stop at a foreign port (a Canadian port of convenience in most cases, such as Victoria) and the closed-loop legal exemption is only for cruises that start and end at the same U.S. port.
Now, with Mom being 80 I would suggest you look at the round-trip when are airline tickets cheapest cruises out of Seattle. You are less likely to encounter rough seas (which do happen on the north or south bound cruises occasionally), and the inside passage is usually like riding when are airline tickets cheapest on a lake for all 7 days.
It will also depend if you are planning to add on a pre or post land in Alaska to see more of the interior such as Denali Park. Most people like to do the land first then sail South. If you are doing a North bound cruise it should be noted that your cruise will actually end in Seward or Whittier, and then you will take a train or motor coach up to Anchorage for your flight home. Princess cruises North bound cruise will end in Whittier and the train is right there making it very convenient. If you are planning only to do a 7-day cruise then a roundtrip when are airline tickets cheapest Seattle would work well and generally has better airfare. You may also want to consider if there are any specific ports you want to visit. If Glacier Bay is on your list then that will narrow when are airline tickets cheapest down what cruise lines and itineraries.