Okay, this is going to sound a little strange, but no; don’t try to be the knight in shining armor.
Romance novels and movies often characterize men as a knight who rides in and sweeps the woman off her feet and into wedded bliss. Many stepdads I know have also tried to fix all the wrongs for their stepchildren. I know it sounds strange but if you try to fix all the problems that other people have created, people may end up turning on you. Come alongside the kids, stepdad, embrace them and try to be a steady, positive influence over time—not the knight in shining armor. Just love them.