At one point Martin is at the surgery with no receptionist, and as he leaves the exam room to answer the phone, many overlapping voices of people in the waiting room call out to him about their problems as he comes and goes. Except most of the actors do not actually move their mouths, and it is clear the voices are a separate recording.
Joan has a sister Ruth who shows up at the funeral. However earlier there as a dispute between Joan and her brother Christopher about Uncle Phil's house and it was split 50/50 between them. There was no mention of another sibling and if there was the split on the inheritance would have been different.