European Sleeper carriages usually have just 3berths per compartment this means you could book 2x2 berths

If you wanna travel in Couchette the can be reserved with 4 bunks in one compartment.

Venice to Salzburg is one of the most popular Routes. You may let us know on which date to assist you and have a look if there are still free bunks/berths :)

Here is a manual how to reserve Austrian Nighttrains on oebb.at with Eurail/Interrail (add the discount & DONT use the seat only option )

Thank you so much seewulf! I am trying to book Venice to Saltzburg in a couchette for 4 on August 1 on the 10pm route that gets in at 4am.  Do you see any options? 

Yes 176€ for 4 bunks in couchette Sleeper is possible too but more expensive.
You may go all the way to Vienna to have a longer sleep on this train.

For some more detail, we all have a Eurail and saw that you could book a reservation for a bed in a 6-berth sleeper. However, I have two questions now that I have bought my Eurail pass:

1. On the mobile Eurail app (Rail Planner) I see a reservation on August 1st but when I go on the web I no longer see a 10pm - 4am train on Aug 1. 

2. However if I look at Aug 2nd, I can see the 6-berth sleeper. But wheat I want to know before I buy this reservation is how we can guarantee that all members of our group are in the cabin. Is this possible and if so, how can we do this?

1.) Never trust the Railplanner app as it get less updates as the Apps and Website of the operating Railcompanies train departs at 9.48pm from Venice s. Lucia (island) or at 10.pm from the Mainland (Venice Mestre)
As shown in the link i posted i recommend to reserve directly with ÖBB (Austrian Rail)

2.) If you book 4berths in a 6berths couchette you will get 2 foreign travelers in your cabin. Cabins in Couchette are mixed sex means male and female travelers in the same compartment

If you book 4 berths in a 4berths couchette you will get your own cabin.

Finally sleepers :)
as there are 4 of you can decide if book 3 +1 one sleeper or  2+2sleeper then you have private sleeper cabins for you.

If you decide to travel in shared sleepers your group will be sorted by sex means Male group members will share their sleeper cabin with foreign male travelers. and female members with other women. :)

My general advise call Austrian Rail and try to get berths/bunks in the middle of the carriage as these are the quiter cabins instead the cabins at the ends above the boggies (wheels of the train) :)
 

Thank you thank you thank you! Your input is so helpful.  I do see now thru the OBB site directly that the cost for 4 in a couchette is 176Euros. I am assuming this is for the 4 people and is in addition to my global pass that we have. It’s not too expensive if that is the case. I will take your advice and call Austrian rail:)

As for the eurail app and website….I am so confused why the information is different from one to another.  My profile has the wrong bday listed on the website but it is correct on the app. I reached out to customer service to see if they can make sure it is correct but haven’t heard back. It appears I will need to have this corrected before I purchase any reservations/validate the pass.  Is that right?

It is important that on the app (which is your ticket) all data is correct. 

Website and App are not connected and don’t have the same data.

Yes-it needs to be corrected.

As we have seen dozens of such reports now-and nearly all come from the Norte Americanos +some other remarks about timings in app for trains: I now start to think it may be that app always uses EUR (central Euro Time) and you are 5-6 hrs behind and hence may still be in the previous day. Even the Brits sometimes get knocked out when they do it just before 23,59 but after 0.00 in CET.

But this is just some ´superstition´ I am no expert at all in IT & all that.