I'm still not finished, but I'm kinda getting close. I should have finished by now, but I had some distractions, including a couple of long phone calls. Below is where I have got to so far. I still have a bit more I want to add, and I'll include scene image descriptors in/with the final version. You can give me feedback on what I have so far, if you like. I'm also curious as to how much mine varies from what you had imagined. So far it's about 100 lines, and might include up to 50 more, so not as long as what you said you had done. If you don't like it and prefer your own, be honest, I'm happy to finish mine, or let you go ahead and do your own version. I want to go crash out for a bit. I'll finish it when I awake.
[cut to the Beth Scene, where she is comforting Morty, at the end of the Planetina story]
Beth: Would it help if Mommy made it feel better here?
Morty: Really? W-what about Morticia?
Beth: It's okay, she's sleeping in the Summers' room tonight. Actually, she was oddly excited about it.
[cut to the Summers' room]
The two Summers are in bed together, chatting, laughing, and being a bit flirtatious with each other
Summer: Your new nightwear looks hot sis!
Summer gives Wild summer a wink. Wild Summer looks slightly embarrassed, but smiles.
On the other side of the room, Morticia is sitting against the wall, that separates that room from Morty's.
She is gently pressing her ear against the wall, trying to listen to what's going on in Morty's room.
Summer: Hey Morticia, I told you, you don't need to sleep on the floor, you can sleep in the bed with us.
As she is saying it, Summer suddenly realises that Morticia is eavesdropping.
Summer: Hey you little perv, are you listening to our brother masturbating, again?
Morticia: E-erm (Moticia blushes)
Wild Summer: God, she really is a little perv.
Morticia: I'm not listening to him masturbating. Beth is in there with him.
Both Summers stop grinning and look shocked.
Summer: Oh my god, is he fucking her again?
Morticia: Not yet, but it sounds like he might be just about to. Do you wanna watch?
Summer: No way, I'm not getting caught, peeping through the door on my Mom and brother having sex.
Wild Summer bites her lip, as she thinks about it.
Morticia: we don't have to peep through the door, Rick invented a one way viewing portal, that allows him to see into other dimensions, but it doesn't show up on the other side, and it works on walls too.
Summer looks stunned and doesn't reply.
Wild Summer bites her lip and softly says
Wild Summer: Fuck yea ... erm, I mean, Dr Wong said it would be good for me to watch someone else have sex.
Morticia sits back against the bottom of Summer's bed, pulls out an odd-looking portal gun from her night bag and points it at the wall. The wall suddenly becomes see through. They can see Beth and Morty sitting on the bed, with his head deep between Beth's exposed breasts, while Beth starts stroking his cock.
Morticia bites her bottom lip as her hand instinctively reaches between her legs. On the bed, the two Summers look on in stunned amazement at the scene in front of them.
Both The Summers lean forwards to get a closer look at the scene unfolding through the portal.
Wild Summer looks at Morticia and realises she is already masturbating.
Wild Summer: [thinks] Fuck, I can't resist. I need to rub my pussy too.
Summer looks at Morticia, and also notices her masturbating.
Summer: Damn Morticia, you have no shame! You're openly masturbating in front of your older sisters?
Summer looks to Wild Summer, expecting her to join in teasing Morticia, but sees that she is also touching herself.
Summer: Fuck! ... You too?
Summer can't resist any longer, she joins in and starts playing with herself.
Morticia: Oh my god! Mom just told Morty she wants his dick inside her, and that he can fuck her raw!
Morticia starts shuddering as she has an uncontrollable orgasm.
Both Summers now have their hands inside their pants, and are fingering their pussies feverishly.
Morticia looks behind her, with extreme lust on her face, and says ...
Morticia: Would you two like some help?
Summer: Help?!
Wild Summer looks a bit confused.
Morticia: [blushing] Well, you seemed to enjoy it the last time I fingered you.
Wild Summer looks a bit shocked
Wild Summer: [thinks] Oh my god! What is it with this family?
Summer blushes
Morticia: Well?
Summer: Yes please ... little sis.
Morticia climbs on the bed and pulls Summer's pants off, and starts to finger her big sister's dripping pussy. As she does it, she gives Wild summer a lustful look.
Wild Summer blushes too, but doesn't hesitate to slide off her pants.
Morticia starts fingering both her horny older sister's tight, wet pussies.
Summer: Oh gawd ... I'm getting close. Don't stop fingering me little sis, make me cum!
Morticia: How about I finish you off with the dildo that Morty bought you, you can pretend your little bro's cock is fucking you to climax.
Summer blushes heavily. Unable to speak, she nods her head.
Morticia reaches under Summer's pillow and grabs the dildo. It slides easily into Summer's soaking pussy.