None of this drama is needed! If you don't like the service simply move your horse and this time pick a higher quality place. Any place that allows boarders to work off board or doesn't have a clean neat professional staffed barn is a
Red flag right there.
That is completely false. There are a number of high quality places that allow boarders to work off board. It can be great for someone who can't afford other options for horse care and for the BO to not have to do all the work herself or hire outside employees.
Call AC, SPCA, and any other animal welfare group in your area, even equine rescues.
Show them your photo's and if you have them text or email records of conversations, maybe record conversations if you can.
Take pictures of the locked up feed, empty buckets, nets, feeders. Of the horses eating wood and manure. Actually video recordings are better if you can get them.
Try whatever you can to make a difference. If AC, SPCA etc refuse to do anything call a local news station, make it hard on the BO, to the point they have to properly care for the animals or the bad press will put them out of business,
All of this. Before you move the horses take photos of EVERYTHING. Grain locked up, with undisturbed dust on the lock if possible, empty feed and water buckets. Filthy stalls if possible. Photos of ALL of the horses from multiple angles showing the degree of starvation. Photos and videos of the starving horses eating their own manure. Try to be sneaky about it so that she doesn't know what you're doing. You don't want her to take things out on your own horses. It's been known to happen. Once your horses are out of harm's way, bring all of the evidence to whoever is in charge of animal welfare in your area. Bring photos of your horses before you moved them there to show them in good condition if possible. There is a chance that they won't be able to do much based on the fact that there's food on the property, but that'll depend on your area. Hopefully the near death horses will be enough to take action.
Try to contact all of the owners that you can, especially the ones that rarely see their horses. Print out multiple copies of body condition scoring charts (preferably with pictures) to show owners and information about the harm which can come from prolonged starvation. Try to convince them that their horse is NOT ok, and encourage them to move to a new stable.
You won't sway all of the owners, but some may be convinced by the BO that their horse is alright. I've seen it happen by well meaning horse people. Heck, it happened to a very well meaning close friend of mine. She began leasing a TB owned by a couple that moved out of the country. This couple left the horse under the care of a trainer, and the trainer starved the horses to near death. My friend was young at the time (15 or so?) and remembered the horse from her youth and wanted to help him. The trainer claimed that the previous owners had stopped paying and she couldn't afford to feed him properly or some lame excuse, and that my friend could lease him and pay for the feed to fatten him back up. The horse was NOWHERE near ready to be ridden (ribs and backbone still showing) but the trainer convinced her that it was ok so she could get the lesson money. She's long moved on from that trainer but still has that horse and having been around horses much longer feels horrible for making that horse work in the condition he was in. He looked much better than he did, but looking back at pictures he was still awful. Had someone other than the trainer been around to talk some sense into her it could have saved the poor horse a lot of uncomfortable riding.
I would also consider bringing legal action upon this person and I WOULD without fail bring legal action if she tries to hold you to giving a 30 day notice. I hope that you have photos of your animals before moving them to the property. That'll help show that the horses were previously in good (or fat) condition and didn't arrive skinny. Since this is the kind of person to neglect horses with a smile on her face I would be moving my horses ASAP and not tell her until the horses are on the trailer and ALL of your belongings are loaded up/off the property. It's the first of the month, so NOW would be the perfect time to split for the sake of your horses. Bad things may very well happen to the other horses, but you unfortunately have almost no say in their situation. Contact the local authorities and anyone else you can, but your responsibility is not to them. It is to your horses. They are your animals under your care, so you need to do what is best for them and get them out ASAP. It'll be hard to leave the starving ones, but you need to look out for your own first and foremost.
Moral of the story: Move your horses TODAY if possible to a new barn. Try to do a thorough job investigating the owner of the new place this time and evaluate the current boarders' condition, but more importantly get your horse out of there. If possible, gather evidence and bring it to animal control. Most importantly, ttake care of YOUR horses above worrying about the other horses. Your guys depend on you!