Hello Shirley
I was on the Lake Garda/Opera tour this year and it was fabulous.
The seating for the Opera evening is on the stone steps inside the roman arena and you are quite high up. As the seats are unnumbered you have to queue to enter and you may not have the whole group sitting together. As you will be sitting for more than 4 hours I recommend you to take your own cushion or get one inside the arena as the ones being flogged outside were of poor quality. There are some more comfortable tiered seating and on the floor of the arena in front of the stage if you wish to upgrade. If you do decide to upgrade there's no guarantee who you'll be sitting next to.
I'm sure you'll have a wonderful time, especially if you get Lisa as a rep!
James