Option 1, while planned, isn’t currently possible. @Elco and co are working on a re-write of the BrewPi software to allow for multiple fermentors & other processes. I’m not sure where they’re up to with that or how long it’ll be though.
Option 2 should work if you install the BrewPi software using the Docker container method which I think is currently the preferred method of installation anyway. You’ll have to make sure each Docker container is set up to its own USB port for the BrewPi itself. That said, I think I’ve only seen people use 2 Docker containers on one RasPi. You might find running 4 pushes the RasPi too much in which case you’d need a slightly more powerful computer. I’d personally choose this option and use an old computer/laptop in place of the RasPi. That of course requires a little more Linux knowledge to get things up and running on something that isn’t a RasPi. But it’s worth remembering that an old laptop essentially has its own built in backup power supply. OK, that won’t stop your heaters/cooling going down, but you’ll still have your temp logging in the event of a short power cut.
Given what I’ve already said, option 3 is the “safest” option. It’ll definitely work. And given the cost of the RasPis against the cost of the rest of your equipment, you might find that the extra cost of 3 more RasPis is acceptable for a setup you can be completely sure will work.