There are 2 numbered doors :
The 5-numbered door and the 4-numbered door.
[9] abducted [4] and makes [4] and [1] to register their number to the 5-numbered door, and then himself.
419 --> 4 + 1 + 9 = 14 --> 1 + 4 = 5
[9] goes alone to the 5-numbered door. After 81 seconds, [9] died from disobeying the 3-5 persons rule per door.
The remainin persons are :
[1][2][3][4][5][6][7][8]
The plan is :
Plan A
4-numbered door : [3][5][6][8]
3568 --> 3+5+6+8 = 22 --> 2+2 = 4
5-numbered door : [1][2][4][7]
1247 --> 1+2+4+7 = 14 --> 1+4 = 5
There will be an option to change the plan into switching [5] with [1] and [4]:
Plan B
4-numbered door : [3][6][8] [1][4]
3568 --> 3+6+8+1+4 = 22 --> 2+2 = 4
5-numbered door : [1][2][7] [5]
1247 --> 2+7+5 = 14 --> 1+4 = 5
I choose plan B. No one left behind just [9] is dead.