Santana has 1 + 1 + 2 = <<1+1+2=4>>4 brothers with birthdays in the second half of the year.
She has 7 brothers - 4 brothers = <<7-4=3>>3 brothers with birthdays in the first half of the year.
Altogether, she has to buy 4 + 7 = <<4+7=11>>11 presents in the second half of the year.
Therefore, she has to buy 11 - 3 = <<11-3=8>>8 more presents in the second half of the year.
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