Story mode, relationships work just like they did there. Free mode, I haven't explored free mode yet so I'm not sure but seeing as how they still make "Theo" the main character I'm loosely assuming it's the same. If you never played story mode, basically you build up talks by sleeping in the same room with a certain girl until you've gathered a certain number of jewels and/or been to certain areas, done a certain number of quests. Then you'll get the marriage event.
Back alley, I'm not sure. My girls from the get go was able to be prostituted but by that point they had at least 100 experiences so that could be a req.
From the description, all the girls must be willing to enter. If even one isn't, you can't enter. Kind of like you fishing for girls in the park or assaulting female adventuring parties. If even a single person is against it due to morals, you won't be allowed to.
I just really hope they learn to lean more on sprite work and not create full CG including background for every single scene.
Would be great if the Inn renovations included ideas from mods like dating, being able to re-see CG instead of just text line, even if it's a one-time event allow MC to get with Maria/Sandra/etc.