Olaf is 12 years + 3 years = <<12+3=15>>15 years old.
Shannen is 15 years old - 2 years = <<15-2=13>>13 years old.
Jack is 5 years + (2 * 13 years) = <<5+(2*13)=31>>31 years old.
The sum of all of their ages is 12 + 15 + 13 + 31 = <<12+15+13+31=71>>71 years old.
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