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From the first two sentences, it is clear that "I", the person who tells the story, is one of sisters.
Let x be the number of boys in the family and y be the number of girls.
Them you have this equation
y-1 = x + 2 (left side y-1 is the number of sisters to "I")
From this equation,
y = x + 3.
It says that the number of girls in the family is 3 more than the number of boys.
Hence, the oldest brother (the oldest boy) has 4 more sisters than brothers. ANSWER
For example the possible numbers of boys and girls can be
boys girls
2 5
3 6
Having this small table, you can check and confirm my final answer.
Solved.