[NEEDS SAVES] Partnered Sims turn into siblings/family relationships

Hi, I recently started having this issue.

Product: The Sims 4 (Digital Deluxe)
Platform: Mac
Which language are you playing the game in? English
How often does the bug occur? Every time
What is your current game version number? 1.105.332.1220

What expansions, game packs, and stuff packs do you have installed?

Expansion Packs: City Living, Get to Work, Get Together, Cottage Living, Seasons, Cats and Dogs, Discover University, Eco Lifestyle, For Rent, Get Famous, Growing Together, High School Years, Island Living, Snowy Escape

Game Packs: Dine Out, Outdoor Retreat, Spa Day, Dream Home Decorator, Parenthood (Every Day Sims Bundle), Parenthood (Pet Lovers Bundle), Jungle Adventure, My Wedding Stories, Realm of Magic, Star Wars Journey to Batuu, Strangerville, Vampires

Stuff Packs: Bowling Night, Luxury Party, Movie Hangout, Tiny Living, Laundry Day, My First Pet, Backyard, Cool Kitchen, Fitness, Kids Room, Laundry Day, Movie Hangout, Perfect Patio, Romantic Garden, Toddler

Add-Ons: Street Eats Digital Content, Awesome Animal Hats Digital Content, Life of the Party Digital Content, Holiday Celebration Pack, Up All Night Digital Content, Bust the Dust Kit, Country Kitchen Kit, Courtyard Oasis Kit, Desert Luxe Kit, Industrial Loft Kit

Steps: How can we find the bug ourselves? 

1. Create two same-sex sims in two separate households - sim A to have one parent and one twin with ability to get sims pregnant, and sim B to have two parents. Play game and gain high friendship and high romantic relationship - become girlfriends, become fiancees, move sim B into sim A household, move sims A and B out together, become wives.

2. Sim B to have science baby with sim A using sim A's twin sister as donor.

3. Sim A to adopt child as care dependent, then clear relationship between child and sim A's twin sister (as twin sister is mother of child - is this a bug???).

4.. Play game, save game, close game, re-open game and resume in sim A's parent household (game closed in sim A and B household - is this also a bug?). Sim A to arrive shortly without being invited.

5. Sim A's mum to give sim A's twin sister a makeover opening CAS (cas.fulleditmode not on) as work from home task while in Stylist career and while sim A is still present on lot.

6. After makeover complete, play as sim A and return to sim A's lot. Bug to occur from this point, when CAS entered with or without cas.fulleditmode on, and when relationships fixed, game saved, then reopened

What happens when the bug occurs? Sim A and B become sisters, grandparent/granddaughters, or aunt/niece
What do you expect to see? Sim A and B related through marriage only with child as daughter of both 
Have you installed any customization with the game, e.g. Custom Content or Mods? Yes, all mods always updated to most recent version after patch updates and before starting game, problematic custom content always removed before reloading game and without saving game
Did this issue appear after a specific patch or change you made to your system? After most recent patch and once makeover completed

Most recent save: Slot_00000008.save.txt