These are two highly anticipated sequels to popular first party Sony games and they should both be showcases of what the PS5 can do. They should push the release dates to 2022 and really use the full power of the PS5. HZD was a showcase of what the PS4 pro could do and the sequel could be the same thing for the new gen console and the sequel to GOW could be as well. Don't make the same mistake CDPR did and release versions that are vastly inferior on last gen consoles.
Last I heard, Sony's been boosting the sizes of their 1st-party studios (Santa Monica, Guerrilla, Naughty Dog) quite aggressively, so they can produce 2 or more AAA titles in parallel.
This is why GoW 2018's Cory Barlog is already working on a new game, despite Ragnarok coming out this year.
If your concern is the amount of resources Sony's 1st party studios can throw at the games to make them "properly next-gen" and coming out on time, that point may already be covered.
For all we know, Horizon Forbidden West may be using a different engine and different assets between the PS4 and PS5 versions.
As for Ragnarok, we don't know if it's coming to the PS4, yet.