What are your travel dated? Milan to Wengen in June could be affected by line closures.
But anyway, you can always just buy a ticket from A to B, for whoever is traveling. The reason passes are brought up is that in some cases passes offer you convenience and/or savings. Good passes for the area you are visiting are the Jungfrau pass and the Berner Oberland Pass. You will have to look in to these yourself to figure out if they are worth it.
Note that it is not because you have 5 suitcases that you need to travel in 1st class. 2nd class is just fine.