Hello Martin, I am truly sorry that you are frustrated, but hang in there. For what it's worth, let me give you my 5c.
Sharon and I had a discussion a short while ago about similar issues. In that discussion I indicated that although I loved Geni, there have been times when I have been quite frustrated when either incorrect information has been loaded, or information gets changed by someone who does not have accurate information etc. There have been times when I have even confirmed a merger based on someone's information and then later regretted that I did not research it myself first. Recently, we had two cases with incorrect information, and Sharon has assisted in getting them sorted.
In the first instance, my fifth great-father had his parents changed to people with a completely different surname. Fortunately, as I had information on his death notice which indicated the names of his parents, Sharon was able to use this document to confirm and correct the information. However, while she was busy sorting things, somebody keep changing details including my great-grandfather's name. Now it could be this person did not know what they were doing, or merely had scant information on something and presumed it was correct and opted to just change information as they saw fit.
The second instance was more to do with similar names causing confusing information. This in turn lead to the incorrect parents being added. Again, we were able to correct using the information on physical evidence from her marriage contract, which listed her parents. Each time, the incorrect set of parents had to be disconnected, with the real chance of losing people assumed to be in the lineage. But rather losing supposed family members than listing incorrect family members.
In some senses, this is the beauty and the curse of Geni.
Now I do not have details about Willem Schalkz van der Merwe's parents, the only records that have been substantiated are from his arrival in South Africa. Everything beyond that is merely speculation until someone is able to supply us with this information. And while we wait for that to happen, it can be frustrating.
I'll give you one more example. I was quite young when my grandmother tried to instill details about our family into my head. At the time, it was not of much interest to me, but I guess it must have birthed something in me. Anyway, after she had passed away, it became more important to me to record what I could. Unfortunately, some things were lost, like a handwritten family tree she kept in her Bible that my uncle now possesses. He denies that there ever was such a thing, but that is a document I distinctly remember because I stumbled over the pronunciation of birth places and the occasional uncommon surname. Some of this information is now lost, but I am hoping not forever. Unfortunately, he also denies the slave heritage in my family...perhaps these are linked? Nevertheless, I had to depend on my memory for much. So, when I started, I did so with what I could recall and searched from there.
My great-grandfather was "blessed" with four names and I knew that his name was Petrus and that Stephanus was one of the four names because it was one he shared with his son-in-law, my grandfather. I also knew that Johannes was in there because of my cousin's name. But the exact order was not so clear in my mind. I knew my great-grandmother's name, and received information from the NG church in Pearston with details of my grandmother's christening. However, my great-grandfather's full name was not used, so I still could not confirm his parents with 100% certainty. I had a suspicion because of dates, but was reluctant to add this to my tree. 5 years later, I managed to find his death notice, and not only did I have confirmation of his name, which incidentally included a Jacobus that I did not recall, but included the names of his parents. With this information, I could finally add the suspected details to my tree.
This is a long-winded way of saying, "give it some time" it will eventually come together and you will learn far more than you could have imagined. But, hopefully, the information you learn is correct and accurate and not assumed or confused with someone else of the same name.
Good luck and best wishes!