Well I worked out that if sally's brother had to have twice as many sisters as brothers I could work it out by seeing the different possibilities of doubling.
Sis. Bro
2. 1.
4. 2 This is the second possibility and it
would work because sally wouldn't be
counting herself as one of the sisters but
Would be counting her brother so 4-1=3 and
2+1=3 so it would be equal to sally and 1
twice as much as each other for her
brother.
In conclusion there would be 7 children in the familily all together 3+3+1/4+2+1=7