In Early Days, Chapter 9, who did the narrator's father want her to meet and how did the meeting go?

The narrator's father wanted her to meet her half-brother and half-sister. The boy was about 20 and the girl was maybe 15 or 16. They came upstairs and the narrator's father introduced them. The boy got frustrated and went down to the lawn. The narrator went down and played with him for a while. Then the girl came down crying, and she and the boy left together.