How do I get this and does anyone know how the party works anymore? It's completely different.
The party got reworked, but it still starts with adding wine and then starting it there.
You can choose, if the mercs can participate or not.
Then you should be able to choose who to dance with.
NEW: You can "Watch" every girl without time moving forward, giving some new reactions.
For Dwain (the merc in the pic with Tia) to appear at your camp, you need to progress Penny's quest: You need to have taken control over the mill south of Arenfield and stationed your men there. Dwain should then show up at camp, if there are open slots for recruitment. You can manage future recruitment with him.
Then just start partying, let the mercs participate and obviously
don't dance with Tia. The scene has 5 steps of progress.
On a sidenote: I think this game has still many scenes and interactions, that aren't covered in the walkthrough. On one hand I think it's cool, because it gives more immersion, but on the other hand it sometimes leads to the feeling of missing out.
I especially noticed this, after I played for the first time, got the whole content and then waited for more then 4-5 updates before playing again. I didn't know small stuff anymore, because there was so much time in between, but I didn't want to play the whole game again, because it takes quite some time to play through.
Having even minor events, interactions and scenes covered in the walkthrough could at least solve this, if one is stuck.