We were in the same boat as you, another couple and their daughter and my wife, son and I will be on the 10 night Norwegian Fjord and Iceland cruise next year.
We decided to give AirBnb a try, first time for any of us. And we have a nice little house (we hope) with a bedroom for each couple and each adult child. We all did a lot of research before deciding on the house we chose; after reading everything about it, location, transportation, sites to see located near by we are excited to check in. I don't know if it is allowable to post a link to the place we reserved or not. If someone else can let me know I can post a link to it.
We too are staying three nights leading up to the cruise.
Just have to figure out the best option for transportation to the port for six plus luggage. If anyone has any suggestions on this it would be greatly appreciated!