How to Tackle Humidity and Smells in My South Carolina Basement?

I'm dealing with humidity issues in my 1900 unsealed basement connected to a crawlspace that sits partially below grade. The front is fully below grade, while the back is about a foot above due to a slope. We're facing condensation and mold problems in the crawlspace, especially where the AC vents blow onto the floor upstairs. There's also flooding near the basement door during heavy rains, and I've noticed mold growing in the basement stairwell. The power switch covers in my house curl up during summer because hot air rises through the walls. Our humidity readings are between 75-85% in summer, although wood moisture levels are only problematic in some areas. Since moving in, I've installed a vapor barrier, sealed external vents, added two 70L dehumidifiers, and set up an internal French drain. I've noticed some improvement – the basement doesn't seem to swell and contract as much, and humidity levels are below 65%. However, the air rising from the basement into the stairwell and walls is still very humid. We've also been experiencing unpleasant basement odors in the house after heavy rains, which wasn't an issue before. We keep a litter box in the basement, so when the humidity rises after storms, the entire house smells like a wet basement with cat litter, even though the basement itself is dry (though the drain is still wet). I'm looking for suggestions on how to handle the rising humidity and those lingering smells – is it an airflow issue? Should we be venting air out of the basement?