Normally you would have to change in Brussels, but there are many trains an hour to Ghent, no reservations needed or available. These are commuter trains, so some are double-decker, annoying with large suitcases. You can stand in the vestibule before the stairs if you are forced to. I would fly into BRU unless it is much more expensive.
You may be able to buy both tickets, or a through ticket in Amsterdam, which will eliminate the need to get in line in Brussels with your bags, for the local ticket. Some people want to visit Grand Place while in Brussels, but maybe that's on your tour anyway. I think Gent has two train stations, so find out which one is closer to your hotel. I think one of them has few trains that stop there.
I BELIEVE that Belgian local tickets are dated, so don't buy extra tickets on your arrival day.
Note that there are three "downtown Brussels" train stops, but all the trains to Ghent stop at all of them. I'd use Centraal because it's the biggest, and has the most services. Some "special" trains like Thalys only stop at the Brussel Zuid/Bruxelles Midi, and that's OK too.
https://visit.gent.be/en/good-know/practical-information/how-get-ghent/ghent-train
https://www.nsinternational.com/en?
You may need a local bus ride to your hotel. Google Maps is your friend. There should be a bus ticket machine outside the rail station, and signposts for the bus lines that stop there. Have euro coins and small bills ready.