Professional travel planners are pretty clueless as far as European trains go. Fortunately, SBB, the Swiss rail company, has an excellent website that is easy to use, https://www.sbb.ch/en. You can get just about anywhere in Switzerland by train, including places cars can't go. Also, except for special tourist trains like the Bernina Express, reservations are not required or even necessary. Also, if you did miss a connection, there are a minimum of one train per hour on every line, so worst case you'd just have to cool your heels for an hour waiting for the next train. You'll find some pretty good advice on this site once you have an idea where in Switzerland you want to go.
Finally, pay particular heed to cj-traveler's advice re luggage. if you could each get by with a single air-line sized wheeled suitcase and a small back pack, life will be so much easier. Maybe take a little down time at your first Swiss destination to visit a laundromat. The girls can help grand ma with her bags.