You may find it's easier if, instead of using luggage, you carry everything in a wearable backpack. Depending on your needs, go with 2,500 to 3,500 cu. in. with at least a couple of external zipped pockets, and use lightweight silnylon stuff sacks to organize some of your things inside the pack. Try to keep weight manageable (20-25 lbs. at most). Practice walking with it before your trip. Once you envision carrying it in a city or to/from the train, or within a train, you may suddenly "realize" there are a few things you can do without. Sometimes less really is more!
The advantage of packs vs. luggage is that it is easier to wear a 25 lb. pack than to carry a 25-lb. suitcase. Once you take what you need or want on board the train out of the pack, its reduced size is easy to store in coach or in a private sleeping compartment. I have no problem keeping my pack at the foot of a bed while sleeping in a roomette or in the overhead luggage rack above coach seats.. If you have an extra unused bunk there should absolutely be no issue for all of you to store your packs there.
If you don't already own an appropriately sized pack, I wouldn't splurge on one that is mountaineering-worthy; you won't be carrying 40-50 lbs. over tough terrain for weeks at a time. You can find inexpensive ones at most of the big box stores that would work just as well for intercity train travel.