So you have 2 problems with the trailer, it seems.
1) The trailer's umbilical connector isn't wired to the modern 7-pin layout, that's causing the wrong signals to blink, running lights to be powered off the 12V
hot line from the truck, etc. E-Trailer has a page that has all the standard pin layouts here.
2) It sounds like the brakes need to be adjusted, or perhaps there's a more serious issue with them. It could also be that the "private party" with the Dodge had the brake controller voltage set too high, but the wheels on both sides of the trailer should lock at the same time if they're adjusted right.
Sorry I can't be more helpful, I'd rather be in cool Oregon (and yes, even though you're seeing 90s, the 50s at night makes it "cool" to this Texan.)
Hopefully someone in OR will be able to help with the in-person stuff.