Hi Detlef,
Nice little collection. I love Congolese weapons and although I do not know that much about them, to me, they are the embodiment of ethnographic weapons
If I had my time over again that is what I would study and collect.
Having said that I have searched for a knife like the first one you posted and have to agree with Colin but the other three look like the real thing to me and could be Saka, Mangbetu and Zande although more knowledgeable members might think differently. Thank you for shaing I love them.
Regards
Miguel