How much does Tessa know about her brother Leonard?
In Episode 10 of FMP, Tessa discusses her feelings of inferiority vis a vis her brother. In the light novel series, it is explained that she is extremely aware of both Leonard's past and that he is working for an enemy organization. E.g. in "Continuing On My Own" he openly battles the Arbalest in the middle of the city and captures Kaname from Sousuke. And for the final showdown between Sousuke and Leonard in the final book, Tessa gives him some words to shout to Leonard at a critical time, revealing to Leonard the extent to which she knows about their family history and his subsequent deeds, distracting and demoralizing Leonard, giving Sousuke the chance to land a killer blow.