So I'm writing my campaign and so far my players love it. I think I wrote the first boss too well because now I'm not sure I can live up to the hype my players are having now.
The first boss was a doctor in a large city that was under quarantine with only five people in quarantine. The players stumbled across her journal only to discover that she is not the town doctor but her husband was, the woman was patient zero.
a false hydra story. The city used to be filled with sick people but when the people died from the illness the hydra would eat them and no one would be able to remember them.
The players realized this and confronted the woman (Ambrose) and realized that she was being controlled by the hydras. The woman truly believed she was the town doctor. but when the players kept pushing her for more information she fell to the ground as a hydra comes up from behind. Ambrose took up a bow and got on top of the hydra reviling to be the first horseman of the apocalypse and had used Ambrose as an avatar (A host of sorts). After a hard battle the players finally beat the first boss only to be greeted with the screams of terror coming from the towns folk who suddenly regained their memories of their fallen family members. although cured the pain of losing your entire family will haunt them forever.

I'm not sure what I should do with the second horseman, war. I know the horrors that war can bring but I'm not sure how to do it. My players are expecting something just as horrific if not worse than what I did with Ambrose. How should I approach this?

I wrote about these for previously, but in such a way that you have to squint a bit to understand why are considered "the horsemen".
The first one, before noticing she was Hefinisna (Death), was a young adult girl into bushcraft and oneirinautics (as you can imagine, things really related to themselves and death XD). Thing is, it's through dreams where her ability manifests: she only has to call the name of someone, and that person most probably will die. And she keeps all the names of everything inside her dreams...
The second one, Nothiss Kaeu (Plague) was a violinist. A great violinist. Heck, even in a city where you wouldn't consider anyone be interested in classics, people followed her. She was "infectious", if you catch my drift. You hear two of her notes and then, sorry for you, you wouldn't be able to break free of her honest charm.
The third one, Berbellum (War) combined male and female, knowledge and intuition, intention and determination... all in one body. They say that absolute power corrupts everything but, what about absolute knowledge? He knew how to cranck the gears of the world to create chaos and change everything without changing himself.
The fourth one, Gura (Hunger) is one i have yet to write. He got the symbol of the scales and turned into his ability: you can be only as strong as he is (or, if you're weaker than him, he can be as strong as you are). He's a bit of a savage, attacking without distiction, but that's probably caused for the events of the story i have in mind.

This is my idea for these four guys. You tell me if they helped you in some way.

thank you this gives me a couple ideas actually