No, the owner is not liable for the actions of the clients; an employer may be liable for damage caused by its employees IF the damage was done in the course of and as part of the person's employment, but is not liable for non-employees or for employees if the damage had nothing to with them doing their job (like with a disabled person suddenly having an episode, which is unrelated to the work they do). You could sue the disabled person, if they are mentally competent and manage their own affairs; or their legal guardian if they are not competent.