[HELP] Character-NPC switch puzzle, The title is confusing.Read the topic to know more. Options

[AphidRuin]

I wonder anyone of you had came across such cases where you have some characters, then you are required to choose one of the characters to a switch, and that character will be stationary there. The others will find other switches and continue this process until all switches are being stepped on, then a certain door unlocks.

For example,

There are four characters: A, B, C, D. They went to an area where a door is locked by 4 switches. Thus, the party went to search and found one of them. A volunteered to stand on the switch. B, C and D will have to find the other 3 switches and step on them like A did. At last, when D, the last and remaining character, steps on the fourth switch, the door unlocks and he goes to find the others before they enter the door together.

My question is: The process when the character turns into an NPC and stands there, how are we going to making it possible? I have tried eventing myself and in the end messed up the whole thing.

Help is greatly appreciated. If any queries about my question please do ask.