I have disconnected the top of the Van Coevorden/Van Bierum family from the bottom of the Von Werl family.
There is no evidence that NN van Bierum ever existed other than the fact that the three Van Bierum brothers must have had a father.
NN van Bierum was previously showing as son of Rotho, Bishop of Paderborn, but even Rotho's own connection to the Von Werl's is tenuous.
If you have any evidence to flesh out this part of the tree please share it.