Partnered Sims turn into siblings

After my sims (both women) had 3 three children (two via birth and one by cloning the second child to artificially create twins), any time I edit them in CAS, they become sisters and the only romance option they have is Offer Massage. I have no idea what's causing this outside of CAS. Things I tried and still had them become sisters:

Moving sims to a different household, editing them, moving them back 

Editing them from CAS via manage world

Editing only the Sim I enter CAS through (like at a mirror or ctrl+click modify in CAS)

I removed all my mods and tried again and, nope, they're still sisters. I found a similar old thread from 2 years ago with no updated information from EA and the sims team. This is a serious game breaking bug that has frustrated me to the moon. 

This bug has plagued my save file. Here's what happened in my game and I think the actions I took may have contributed to introducing the bug in my save file:

I created a fresh save and then created a brand new sim. Her name is Lynn and she's a young adult.

Lynn partnered with Olive Specter, an adult.

I moved Olive into Lynn's home in Nordhaven and aged Olive down to teen. I then saved and exited the game. The intent for my gameplay was to have two teens living together by aging Lynn down too but when I re-entered the game to age Lynn down, they were listed as siblings with a full romance bar.

All attempts to correct this failed. I researched if other players had same issue and tried their suggestions to no avail. I even created parents for Lynn and Olive (neither had parents in their trees), moved the parents into the household, deleted the relationship via MCCC and the bug was still there upon reloading the game. Finally, I gave up and had to dissolve the romantic relationship and leave them as siblings.  

Call me crazy but I believe the factors that brought this bug into my game are: same sex couples, aging down Olive to a teen in a young adult's household (the game doesn't like when a teen doesn't have parents, so it chooses a guardian for them..?), and Olive being a pre-existing sim. 

I wish I could help by submitting my save file but I have waaay too many mods and cc and I cannot verify whether any of the mods may or may not have contributed to this bug. I hope this explanation helps in lieu of my save file. Perhaps the Sims Team can reproduce the bug in a vanilla game.

Did you fix it? I have the exact same problem 

Hey all!

We've been trying to reproduce this issue internally and still haven't been able to do so.

If you run into this issue it would be a massive help if you could provide us with your latest ".ver" backup save file so we can see what is happening just before the issue occurs. 

Info on what (and where) .ver files are can be found here, steps on sending files are right here. 

Thanks!

Oh, sorry, I've already deleted this save file

:(

But I'll try to see if I can trigger it again after I get home from get off work.

Okay, I failed to trigger this bug again.😕

I already did it

Hey there Wan_FengLin​ 

Would you be willing to share a save file with us from before this issue occurred in your game to help us investigate into this a bit further? 

If so, please send me a private message with a link to the file. Instructions can be found here: [INFORMATION] How to Send User Files to The Sims 4 Team 

Thank you! 

Yes. I am playing a lecacy, both affected sims have 2 parents. I can completly remove their relationship bits with cheats, but the only thing that will not completly reset my work for a decent ammount is replacing one of them.

w31nerbug​ are you giving the couple parents when you replace them? That's the only thing that has helped me. 

Hey, I'm  not sure if you were able to fix your issues, but you might need to start the save afresh and see if that affects it, otherwise, you may need to manually reset their relationship in CaS with "Cas.Fulleditmode" enabled.