That will depend on the size of your suitcases. 4 with size "cabin trunk” will be difficult, but otherwise you should be OK.

Thank you - not sure what a cabin trunk is? Will have 2 medium pull along cases - am wondering if they will stand upright in the middle of seats/couchette beds?

There is usually luggage space above the corridor and below the bottom couchettes. It may also be possible to leave one suitcase on the floor, e.g. behind the ladder. See e.g. this page to see what a compartment looks like, although it doesn't show the space above the corridor.

Google will show images if you look for "cabin trunk” :)