Having traveled around Switzerland on their marvelously efficient trains, I think you're making a great decision to use them! And with the luggage of 4-5 people, you may have found it difficult to get everyone and even their small suitcases into a single car.
Regardless of train or car; traveling light is certainly one option and will be strongly encouraged by anyone who packs light and does laundry periodically. Many hotels will do laundry for you or have facilities for you to do it. Still, it took me numerous trips - and a few mishaps with big luggage - to learn my lesson and get the hang of packing lighter.
With more or bigger bags, I would caution that you not be in a rush! At least for me, that's when I got tripped up and took a fall that, fortunately, was nothing more than a mishap and didn't put a damper on the rest of my trip! (My Mom thought for sure I'd busted my knee and ruined my entire vacation.) It's one thing to test drive carrying your luggage across your living room. It's another altogether to carry it when you're rushing up and down stairs and across uneven surfaces to catch a train.
Next, I would suggest that you have a system for getting on and off the train with your bags. You'll want to be able to embark/disembark efficiently - depending on how long the train is at your stop. Work your way towards the train doors (with luggage) well in advance of your stop. Perhaps one person (or 2) gets on/off the train and someone else hands the luggage up/down. Before the last person embarks/disembarks the train, count your bags on the platform/train to make sure you have them all.
If you'll be walking to your accommodation, make sure you have a paper or electronic map from the station to each hotel/Airbnb.
If you'll be taking taxis, you may wish to research those ahead so that you know the recommended taxi companies and where to find them. You may also be able to arrange pickups with your hosts, in which case you'll want to alert them to the # of bags.
If you have any tight train connections, you'll really want to make sure that you're able to move smoothly with your bags.....up and down whatever stairs and uneven surfaces there may be between platforms or at the stations.
If you're able to do any sort of "trial pack" - even if you just load up your suitcase to simulate a full load - I'd suggest that you take that out somewhere and drag it around a bit to make sure that you really can carry it under the conditions of train travel! That may help you decide whether to take that "one extra outfit" or leave it behind!!