Vee has an idea... and it's a good one. (TheFallacyGuy)

"Well..." Vanessa starts up: "since I got Asta's first kiss-"
"And second." Olivia interjects.
"...and second, right. I think it's only fair that Ollie gets the first time..."
Olivia blushes at her sisters request.
"And after that," she continues: "We can just take turns."

You know that you just said that you would stop worrying about it for now, but this is still kind of weird, right? This is not a normal situation, this isn't a normal conversation. You don't talk about this kind of shit at the water cooler.
"Oh hey Jim, how's it going?"
"Hi Astrid. It's going fine, the wife is still nagging me about buying a new dishwasher, but you know how it is."
"Yes, yes."
"How about you?"
"Oh, you know, nothing special. I just had a couple of homeless sister moving in over the last couple of weeks, and we've gotten really close. We kind of had a bit of trouble of figuring out who I was going to fuck first, but luckily I think we found a proper solution."
"Ah, I see, so, we're still on watching the game on Friday?"
"You know it."
This is fucked up beyond belief, and you can't really believe that you're getting away with it. Not only that, but they seem more into it than even you are, and you're not exactly finding making love to two gorgeous and kind and smart women to be an especially unpreferable living situation.

"Is... is this real life right now?" you ask just kind of defeated.
The girls just laughs at your disbelief.
"Should we take that as a 'yes' Vee?" Ollie teases.
"I think we should." she replies.
"I... I... I need to sit down." you say.
"You ARE sitting down." Ollie corrects you.
"Right. Right."
"You are not going to pass out again, are you?" Vanessa asked worriedly.
You might as well at this point.
"The colour is disappearing from her face again, Vee!" Ollie is starting to get nervous.

Okay, Asta, old gal, pull it together. Breathing exercises. Count from ten.
Ten
Nine
Eight
Seven
Sex... six
Five
Four... nicate
Three
Two
(B)one...
Zero.
This is not helping.

"Astrid!" Vee and Ollie yell in unison taking you out of your trance. They have apparently been trying to get your attention for a little while.
"Yes... yes... I'm okay."
You think that you've gotten over the worst.
"You sure?" Vee asks.
"Yeah." you reply.
"Okay... then I think you and Ollie should have sex."
"What?" Ollie asks surprised.
"Like... right now?" you ask.
"Mmhmm..." she just answers.

Vanessa is a bit of an odd fish. She is so super shy and reserved with all aspects of her life, but as soon as sex is the subject of choice she is being extremely confident and open.

"I just thought we agreed to not rush things." Ollie states confused.
"I know." Vanessa states: "But I really do think that it's both healthy for us as a relationship, and you as a person, Ollie, if we just get to this part as quickly as possible."
"How will it be good for us?" you ask.
"Well, it would close the final gap of our intimacy. If you have sex with both Ollie and I, we will finally get over this last hurdle in our relationship and we can start to enjoy and revel in our new found love and we can finally aim for some stability without constantly being in fear that we step over each other's toes. It will also be good for Ollie to finally get some experience... and I guess for you too, sweetie."

It really seems like Vanessa has thought this through. While Ollie and you have just treated this issues like a game of Chinese checkers, Vee has shown her true colours by revealing her 3D Chess board...

"Also... I really want to make love to you."

...or maybe she's just really horny.