Regarding the WT illustrations referring to Chimpanzee skull and Extinct Ape skull, I think I have found an explanation. a number of online sources mention that William King Gregory was curator at the American Museum of Nations History (the same museum mention the Evolution book regarding the extinct ape). https://www.researchgate.net/figure/Evolution-of-the-human-skull-The-William-K-Gregory-model-American-Museum-of-Natural_fig12_304906891 makes use of source by Gregory in which an "Anthropoid (Chimpanzee" skull is used to illustrate on the stages of evolution toward mankind. The shape of that skull bears resemblance to the one in the two WT books. The one at https://wellcomecollection.org/works/au6kdyhx (using Gregory as a source) bears very strong resemblance to the one in the two WT books. The latter source identifies the skull as "Anthropoid (female chimpanzee)". Another source with the same looking skull says it is a juvenile female ape (I don't have the link for that source at this moment since I am making this post away from my home computer). This is not a male skull (whether juvenile or adult) and not an adult female skull, but a juvenile female chimpanzee skull as illustrated by William King Gregory. I doubt Gregory was claiming humans evolved from chimpanzees, but rather was saying that an extinct ape that humans evolved from had a skull resembling that of female juvenile (but not likely infant) chimpanzees. I suspect that the later two illustrations are in Gregory's 1951 book called "Evolution Emerging: A Survey of Changing Pattern's from Primal Life to Man" (I recall an online source referring that book as a source for illustration used on the online site). Furthermore, since in the 1960s many evolutionist anthropology books said that Ramapithecus was a hominid and a human ancestor (partly because the teeth discovered of it by that time resembled human teeth [the front most teeth, including the canines, not yet being found]), ideas about Ramapithecus teeth might have been used to make a reconstruction of the teeth of a presumed extinct ape ancestor of mankind and maybe including it in the illustration that the WT had access to.
Furthermore, a book (by Robert Jastrow, I think it was the one called "The Enchanted Loom: Mind in the Universe") quoted the WT's Creation book, has an illustration of a presumed extinct ape ancestor of humans. A footnote for the ape skull in the lineage says that the a chimpanzee skull is used to represent what the extinct ape skull looked like.