Krist Abraham · Somsak Jeamteerasakul Prem is an aged enemy, too weak and too old, whereby he has nothing to lose and nothing to gain for, to fight with. His best bet is to leave Prem faded away harmlessly. At worse, he could send him some form of peaceful rest without a widespread fighting.
I am sure Prem mansion and other bud-heads are under heavy surveillance. In other words, the mercenary team is already at the door way of everyone. Should someone makes a move, he will be eliminated preemptively and swiftly. Thank for the move too. Because it gives a justification to step up with a victory.
So if Prem thought he was a regent and tried to act otherwise, he will be checked and replaced by someone else soon, and he would be punished quietly later. Because the becoming king is already IN CONTROL.
You are a historian by profession, so you are supposed to know better. The 'move today' suggests many. But overall it suggests that this is the same game of selective purge when king Taksin was overthrown two hundred plus years ago. The rest might be similar, subject to the incurring facts.