Shorex

I'll leap to my personal opinion of the "best" cruise line for the South Pacific: Paul Gauguin. https://www.pgcruises.com/ Explore the website, click each tab at the top of the home page, and see how their cruises immerse you in the culture and beauty of the South Pacific. I especially like this itinerary: https://www.pgcruises.com/marquesas-tuamotus-society-islands-n031222-1 And Air New Zealand has plenty of flights to/from Tahiti and Australia.

I agree with Idubs, don't try to force them into being someone they are not. From your description they will be out of their comfort zones. Just have a pleasant first day dinner, chat about the activities that are available and be relaxed. The more relaxed and casual you are, the more relaxed they will become. Let them bond naturally, maybe, just maybe, they will become close friends.

Seabourn provides a packing list: https://www.seabourn.com/en_US/luxury-cruise-destinations/antarctica-experience-packing-list.html That's the list for the expeditions. On board the ship, here's a general packing list and dress code: https://www.seabourn.com/en_US/packing-list.html If you don't want to dress in formal attire for The Restaurant on a "formal" night, there are alternative dining options. Other than that, the Seabourn discussion board is a great resource for asking questions.