Re: Sims won't interact with objects; CC works individually, but not all together.
Wanted to post an update to this as I have finally found the issue!!! (I have only had the time to sit down with it recently)
Somehow, there actually was a conflict with some of the mods/cc that I had had installed for years. I used the Mod Conflict Detector by DmitryMalfatto on Mod The Sims (no idea how I missed this before, since I had looked for broken mod detectors many times in the past), deleted the mods that it said were conflicting with some others (Ikea curtains and some eyeshadow, of all things), and my Sims will now interact with each other as well as objects. Yay! I'm so excited to finally play this game again after months of being without it!