17 year old and 15 year old will be fine with rollercoasters. 12 year old is timid. At Lagoon I had to bribe him to get him on Colossus, he loved the white rollercoaster, wouldnt even consider Wicked or Cannibal. 8 year old is a bit more daring, he did Colossus before the 12 year old but he had zero interest in even considering Wicked or Cannibal as well. 5 year old isn't tall enough for big coasters.