If you don't have a contract, be aware that they could tell you to pay more or get out. I understand how inconvenient it is to travel to see my horses. My last boarding barn was 50 minutes from my house. Having to have someone else with you makes it twice as hard.
But it is worth it to you to put your horses at risk like that. You're potentially asking for huge vet bills or worse, injuries that can't be fixed and your horse has to be put down. That can happen at any barn of course, accidents happen. But it sounds like the chances of an accident occurring is very high.
Do you always need to have someone there with you while you work with your horses? Maybe you can consider only ride one day a week when someone can come with you, and doing ground work, longing, etc other days of the week while you're alone.