Okay so here's what happened.
Holy crap! Glad everyone (horses included) made it out fine. Yeah the chains aren't a 100% safety feature, just meant to be a failsafe in case the ball pops off. I wonder if they shouldn't have designed that trailer with heavier chains though? Tough call...
Trailers need to be approved every second year to refresh the street permission. How's the frequency at yours?
Never. Literally once you register it you likely never need to bring it for inspection. Larger trailers and commercial units are different. Also not sure about trailers for carrying animals. I do know that boat trailers, sled, utility etc. basically have no inspection requirements unless they're brand new.