I highly reccomend finding your own route to the ending using these hints first, but if you are still stuck, there is a full walkthrough below.
This should be sufficeient to have sex with Dylan, Violet, and April, then receive the threesome in the epilogue.
Speak to April & Violet (not Dylan)
"Hey, gorgeous girls."
"I missed you too, Violet."
"Yeah, we totally had a foursome once."
"I'm (name). You're lovely,-I mean, it's lovely to meet you."
"So, where do you sleep?"
Enter the bathroom and have a shower
Don't go to bed. LEave your room and head to reception.
"Nice. An evening's always more fun with added Violet."
"Anything you want, V-girl!"
"I'll always remember my V-girl."
"Sounds like Dylan has good taste."
"Don't worry about it. Just give me some too."
"Violet's always the centre of attention. I'd rather talk about you."
"Because you're really cute."
"No. And it's girls. I definitely prefer girls."
"I really like the sound of where this is going."
"I was really hoping you were going to say that."
Take Violet to her room. Leave straight away.
"I'd carry you to bed if you needed it."
Kiss Dylan when she propositions you.
Have sex with Dylan
"I see you still like swearing."
"For you, anything."
"Why don't I check my car's tank?"
"I could walk that."
"Sure, as long as I have plenty of water."
"No, but we did see some sand, more sand, and....more sand."
"How about me and Violet?"
Use bed or Walk around the motel then sleep.
"Hi April. Nice outfit."
Stare at her legs
"Hell yeah, I'm staring at your legs."
"You know if you were naked, you could say exactly the same thing."
"I've the money, but I don't have the water yet."
"Hi, Dylan. Violet said you had some water to pick up."
"You too, Dylan. I'd hate for anything to happen to you while I'm gone."
"Yeah, let's find something to talk about."
"Sure, if you want to."
"Really? I...I do miss her a little."
"We come in peace!"
"Maybe the size of your boobs was intimidating and they all ran."
"To be fair, there may have been a zombie apocalypse and he killed all the zombies."
"It's OK. I'm here."
"Hey, if any of those monsters turned up, I bet we could kick their asses."
"Why don't you strip naked are run around a little? That always cheers you up!"
"You heard. Strip naked and run around. It'll 'boost your confidence'."
"See. I know exactly what cheers you up."
"April's a lucky woman."
"I'm sure she'll love it."
"I would love to fuck you."
Have sex with Violet
"Quick. Check it."
"Yes! We are gods now!"
"Damn right. Let's go as soon as we can."
Any response until end of part 1
"We should find Dylan. Maybe she'll know what's happening."
"We should check all of the rooms. For Dylan, or sword weilding creepy guys."
"I vote for drinking too. I think we all need it."
"Trust me. You'll love it."
"Of course. You deserve the best. By which I mean strongest."
"I think she likes it."
"Only if April goes first."
"I think April's version was a little more...credible."
"I think it deserves an A."
"Go for it, V-girl."
"It's OK. As long as we're together, we'll be fine."
"Sure. Anything for you."
Follow April to her room
Watch her for as long as you can.
"Yep. And yes, it was very hot in case you were wondering."
"I don't know yet, but we'll find it together."
"Then we'll bring it down to our level and punch it in the face."
"Yeah, we already did. It was hot."
"So have you."
Have sex with April
From here's it's impossible to fail. You should always end up with the threesome epilogue.