jmc

Solution 1: We choose any seat for Pierre, and then seat everyone else relative to Pierre. There are 2 choices for Thomas; to the right or left of Pierre. Then, there are 4 possible seats for Rosa that aren't adjacent to Pierre or Thomas. The five remaining people can be arranged in any of $5!$ ways, so there are a total of $2\cdot 4\cdot 5!=960$ valid ways to arrange the people around the table.

Solution 2: The total number of ways in which Pierre and Thomas sit together is $6!\cdot 2=1440$. The number of ways in which Pierre and Thomas sit together and Rosa sits next to one of them is $5!\cdot 2\cdot 2=480$. So the answer is the difference $1440-480=\boxed{960}$.