1.) why do you think identical twins look so similar?
2.)most brothers & sisters don't look exactly the same. what causes most siblings to have different appearances?

Twins share the same genes, but siblings born at different time does not share the same genes. 

Identical twins look so alike for a reason. The alleles that were passed down to the twins were the same amount, and that means that the traits are the same as well. Brothers and sisters do not look exactly the same because the alleles that were passed down were probably heterozygous genes, which means that we get the alleles from both parents. Hope I could help you!