First, let’s start off by removing the two that don’t a a brother or sister. That leaves 10 people who do. The we calculate the access answers. They go in the middle. It’s 6. Then we have one more that has only a sister, put that at the S side. Then we have 3 more left that have only a brother, put them on the B side. Then you have 10 dots on the diagram for the 10 peoples that have a brother and/or a sister.
To conclude:
3 on B
6 in between
1 on S
