For your couples struggling to be friends, you might try this solution that I use. I had this same problem across all of my households and it was ridiculous because my couples truly belong and want to be together, yet every time I would load into a household, they were all very unsatisfied with their relationships. To combat this I find that making sure both sims complete the Love aspirations of Paragon Partner, Romantic Explorer and Soulmate. Having all of those was a game changer. However, it can really be a pain to get them all without using a mod because some of the parts conflict and/or, doing it on one sim doesn't complete it on the other sim even if they're at the same stage of the aspiration. You can use sims outside the relationship to get credit, like asking about romantic boundaries, but I think I only tried that once because I was worried that it would count as cheating or something. Also, completing all three aspirations is very time consuming per couple so I found a mod called UI Cheats Extension that I will use to quickly complete the aspirations by opening up the aspiration and right clicking on each task.
I don't like to use mods either but unfortunately some things can't wait on a fix to come out and this is one of them. Once I am done I save my game and exit, remove the mod from the mod folder and restart my game. I just keep the mod handy to pop back in to the mod folder as needed. I hope this helps you if the problem is as bad for you as it was in my game.