What works best is making them part of the "process" that is talking to them about what's going to happen, let them choose sheets, etc.
Once the bed is set, you just lay Dorian there and tell him is night time and leave. He might stand up and you redirect him to his bed, the first time you explain him it's night time and we need to sleep in our beds. Following times, you just keep redirecting him without eye contact or talking, just soothing with your presence every time he jumps out. It might turn into an exhausting couple of nights but in the end, he'll understand that he's not supposed to climb out of his bed. Some moms put a baby gate in the door, it works for some, but for others, they just find this gate leads the baby to cry even more so he gets mommy/daddy to come and get him.
It is important to have in mind that this might turn into a 2 week period of not much sleep for all the family. Since Chase will be in the same room, he might get upset at loud nights. Do this transition when all family is ready for sleepless nights (maybe this coming summer when chase doesn't have to attend school?). If you think it is too early for Dorian to make this transition, by all means, hold on till you guys are all ready.
There are also some posts around here about switching to toddler's bed. You might have to surf through the board but they might be helpful for you to find another helpful insights.
HTH! and good luck!