Scandinavia

Welcome to the forum.

Best is that you search in Trip Reports and the forums of the Scnadinavian countries for travel experiences and create an own itinerary which you write down here and ask special questions or for general feedback.

An exampe from Sweden forum which lists some main travel options.
https://community.ricksteves.com/travel-forum/sweden/denmark-norway-vs-sweden-finland-for-first-scandinavia-trip

In best case add preferences, interests or things you identified as a must-see for yourself. Also preferred way of traveling as well as size, age and fitness of group can help to do recommendations.

The visitor websites of countries, towns and regions can be very helpful, e. g. Visit Norway.

Scandinavia is more than city visits only - it is also nature and outdoors.
October can be stormy, cold and wet in Scandinavia.
Chances for Northern Lights.

When is the beginning of October? You have 6 towns and cities in around three weeks which is a bit rushed. And Tromsø is very much the odd place pretty far from everything else. Do you have a special reason for including Tromsø?

Arriving the morning of 30 September. Yes, it is a quite a lot to squeeze in but we are coming from Australia and trying to make the most of what may well be our only visit to the region. Tromso was included as there looked to be some fun activities and, again, unlikely we will get another opportunity.
Happy to hear suggestions.
Thank you

25 days is more than 21 days. What fun activities led you to include Tromsø? They might be available in other places that are a bit closer. It would also be helpful if you told us a bit about what you're interested in and what you want to see and do.