Brothers and Sisters

It may look like there are 5 siblings, but that is not the case!

Because statement A says “I have 3 younger sisters”, there are at least three girls. Because statement C says “I have 3 older brothers”, there are at least three boys, thus putting the minimum at 6. This minimum does not change with statement B, but we need to verify that such an arrangement is possible.

A has three younger sisters and C has 3 older brothers so if you make a chart, it could look like this:

Male, Male(A), Female(B), Male, Female(C), Female

Another way to look at the problem:

A) 3 younger sisters, 1 older brother

B) 2 younger sisters, 2 older brothers

C) 1 younger sister, 3 older brothers

It can be viewed as a table

Case A ) sis < sis < sis < [A] < bro

Case B ) sis < sis < [B] < bro < bro

Case C ) sis < [C] < bro < bro < bro

There's one youngest sister, and one oldest brother. C is the second youngest sister, and A is the second oldest brother. B could be either male or female.

If B is male, it needs to be older than two sisters and younger than the third one.

sis < sis(C) < bro(B?) < sis < bro(A) < bro

If B is female, it needs to be younger than two brothers, and older than the third one

sis < sis(C) < bro < sis(B?) < bro(A) < bro

Either way, there will be six siblings.

Person A is a male, has one older brother and 3 younger sisters. But he also has one younger brother (even if not mentioned); as it is required in statement 3 (we'll see below).

Person B is a female, she has two older brothers (person 1 plus person 1's older brother), and two younger sisters; and she herself is one of the 3 younger sisters person 1 has. She also has a younger brother, not mentioned in statements A and B; but required as explained below.

Person C is a female, but she's the 4th in the family, having a brother that is younger than person 1 (and who IS NOT mentioned in either of first two statementes, but needed since she has THREE older brothers). She herself is one of the three younger sisters of statement A and one of the two younger sisters of Person B.

Hence, there are 3 brothers and 3 sisters; but in this order: B, B, S, B, S, B, B. That's the minimum way all three sentences above can be true.