They're a decent challenge, but far from unreasonable. From what you've said it definitely sounds like you could manage them. Bloodborne is definitely the better game of the two overall - it's got more variety in enemies, areas, bosses, weapons etc., it's better balanced, and the world/lore are far, far better. Nioh has deeper core combat, but suffers in other areas, particularly lack of enemy variety. If you play one and like it, though, I'd definitely recommend playing the other, as well as the Souls series.