Damn, I love the term "meta", and generally enjoy meta concepts (metamodernism, metacognition, metaverse, metamorphosis, etc.). This taints the term terribly.
I'm not sure how the structure is, if Facebook, Instagram, WhatsApp and Oculus are separate companies owned by the holding company also named "Facebook".
Obviously the websites/apps will keep their names, just a design will change, e.g. if you load Instagram, the splash screen says currently "Instagram, from Facebook", and it'll be "... from Meta" soon enough.