Final answer:
The therapist should politely decline to discuss personal matters and maintain professional boundaries.
Step-by-step explanation:
When a client's family asks the therapist about their private plans, the therapist should politely decline to discuss personal matters (b) and maintain professional boundaries. It is important for a therapist to maintain confidentiality and not share personal details with clients or their families. Sharing personal information openly (a) can blur professional boundaries and compromise the therapeutic relationship.