The operative word in this question is "dementia." A person who suffers from dementia does not have the same reasoning capabilities that he or she once had. If your parents
are suffering from dementia, they are not able to process information, or understand cause and effect. Refusing help is common for those who have dementia, and it only gets worse as the dementia progresses. That refusal eventually can manifest itself as refusing assistance in toileting or personal cleanliness.
The challenge here isn't getting your parents to accept the facility's demands; rather, the facility doesn't sound like a good fit for your parents. You need to find a housing solution that better meets their needs, such as a memory care community. I would also recommend reading about communication with people with dementia, as the techniques that work best are often counter-intuitive -- they're the direct opposite of those that are effective with a person who is cognizant.