Well father/daughter attraction is a real thing. The only reason it doesn't happen is human cognitively train their brain that it is a no go zone. They are afraid of consequences like birthing retarded children or death or hell fire.
But for a gaaalo like Musk senior- there is no stopping him. He is a victim of this father/daughter bond/love that is more powerful than any love, except the mother of course. Remember Musk senior is the first point of reference for her as who men are. The sex happened in 2017- no doubt the daughter seduced him, and he like any other man fell victim. The step daughter is a gold digger