Do you have more steps? "Open to advice" is a bad approach to ethics. Perhaps hire a consultant?
Screening volunteers to deal with the elderly is a fairly standard process for hospitals and care homes. Maybe interview a few of them on how they do it?
I think they do it by running background checks and meeting the job applicant in person. That wouldn't work very well for remote-only work that recruits people from anywhere. I don't see how you could vet people with anything approaching due diligence without eating up most of your first few months worth of fees up front.