Guys, I don't understand what the problem is? If you know how to solve the problem, then why don't you just help? Is it really that hard?
You asked for a walkthrough for Katherin, yet your Katherin is already pregnant?
Which means you wanted an hour of my time to type up information that would be useless to you. So when that is a possibility, you most often are going to get ignored. I don't even think I could type up the whole walkthrough without forgetting a whole bunch of steps, since I only have done it a couple of times. And I wouldn't even be able to type any of it up for the Dasan as chieftain route.
What is the current quest directive telling you to do? Answering that issue is easy, starting from the beginning is me grinding for your sake, when you haven't even taking the time search for your specific issue, or ask it, just "type up everything you know about Katherin in Rumah". Most folks aren't going to take the time to do that. It's on you to either search for the answer, or make it easier for people to help you.
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If I am understanding your last question correctly, you have "talk to Tia while in Rumah" is that correct?
You said that Katherin is pregnant, does she know it? You can see the animation right away, but the LI's don't know it for 5 (I think) days. So you the player knows it, but the MC and LI don't.
Does Katherin know it? Have you talked to her about it? If not, wait a few days until you get the notification about Katherin being pregnant down at the bottom of the screen. Then go talk to her.
She might have to be in Rumah. She only comes to Rumah every two days (Home, Home, Rumah, Home, Home, Rumah, etc.) at 5:00 pm, there is no way to track it, since it changes days of the week each week. (Mon, Thurs, Sun, Wed, Sat, Tue, Fri, repeat). The quickest way to find out is to go to Rumah, skip to 4:00 pm, skip an hour, if Katherin doesn't immediately start walking in the main gates towards Tia's hut, it isn't a Rumah day. So you have to skip a day until you find her there.
After you talked to her about her pregnancy, then go to Tia's hut and sleep with them both. That should end the current content for "Katherin's pregnancy", it doesn't sound like your save has any Katherin content left at this point anyway.
Maybe the fifteen minutes I spent typing up the narrower answer to the issue of:
she is already pregnant hlw to convince tia ?
Katherine is already pregnant, but there is no progress beyond that.
Answered your question.
But maybe I wasted that time because your issue is something different. The more you narrow down your specific issue, the more likely you are to get someone to try to help you.
Asking for the full walkthrough means I don't know if you don't know how to initiate the quest to get Katherin to Rumah, or maybe having an issue with Nyra, or Dasan. My not knowing that answer, I am going to ignore that herculean ask for my time every time, and most folks are going to as well.
So that's the issue at play here. Make it easy to help you, not hard.