Both Bruce and Rosa want to avoid the constraints of uchi, although for different reasons. Rosa wants to save her busy okaasan from having to drive her to the station. Bruce is not having a good experience with his homestay and wants to avoid bothersome constraints like tatemae/honne and uchi/soto. He feels he can do this by making friends with Japanese whom he feels are similar to his friends "back home". Yet even though Bruce's friends have studied abroad in his country, his friendship has striking resemblances to the homestay relationships outlined so far in Part 3. Although his friends speak and act informally they still cater to his demands and help him out, even when this means canceling an important date. Bruce doesn't notice how much they defer to his agenda, however, and seems to see this as "normal life". This should bring up images of Peter for you.
Uchi exists not only in families, but in work teams, schools, and even among groups of friends. In Bruce's case, his friends' uchi centers around Kazu, and the parties they all attend at his apartment. Just as in the family, his friends expect him to reciprocate the indulgences they have extended to him, by gradually accepting the responsibilities of uchi, which include attending the parties, and thereby "moving into" uchi. In refusing to attend the party, Bruce acts only from an individual vantagepoint, failing to take uchi into account. This failure resembles Theo's bicycle problem, Sophie's problem in accepting the ride, and even Janine's "test" with the otoosan' s guests. It's for you to decide if Bruce is really doing okay with his new friends, or if he's missed the hazard signs and started heading off the cliff.
Rosa manages to ignore her okaasan's role (and sphere of competency) in the household. She also considers her relationship with Mira from an individual standpoint, rather than from the standpoint of uchi. From that standpoint it was the uchi okaasan's obligation to take Rosa to the station; not that of a soto friend. This case also resembles Theo's bicycle situation in Module 8.2.