Thanks for the informations, Jürgen!
I think that two options influence the strenght of the rodent personalities most:
First: NpsLimit (nodes per second)

The correlation between NPS an ELO-Strength can be found in the Lucas-Chess Documentation (
http://lucaschess.pythonanywhere.com/):

So by reducing the NPS of the above named engines their strength can be adapted.
Second: EvalBlur
I think with this parameter you can influence the tendency of the engine to make "human mistakes".
With this in mind I will try to adapt the personalities to my desire.
Jogges