I was able to identify the third and last dagger I described. Here they are again :
I had a look around on
http://www.mambele.be/ and I think these two daggers can be attributed to the following tribes from Congo : Ngombe, Doko, Ngbandi or Mbudja.
As to the dagger with the slender blade, I'm still guessing.
Does anyone has a suggestion ? It would be much appreciated.