You can decrease Ada's lewd level with herbal tea. You can buy it from Sand Town's oracle temple after advancing the plot far enough.
Well, you get normal scenes by default before reaching a certain lewd level's threshold. After this, you'll get lewd variations. This is true for both combat and mansion scenes.
Baron's mansion has a cellar and it's one of the H scenes from it.
There's no correct strategy for Yorna, just adapt your current build and get more magic defense is the incoming damage is too high.