Travel in and around Germany, France and Italy

Which would be the best way to see all 3 countries? We have 2 weeks but probably just need 7-9 days of train travel. We are traveling in August. This is our first trip to Europe and we have family in Germany but would like to travel by train in all three countries if possible. 2 adults, 18yr old and 16 yr old. Which class of service is best?
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