Ella wanted 2 while Emma wanted 2 so 2+2 = <<2+2=4>>4 hotdogs
Luke could eat twice as his sisters so 2*2 = <<2*2=4>>4 hotdogs
Hunter could eat 1 1/2 times the amount of his sisters so 1.5*4 = <<1.5*4=6>>6 hotdogs
All total, Matthew needs to cook, 4+4+6 = 18 hot dogs
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