A guardianship agreement is legal document which sets out who should be your guardian should you no longer have the capacity to manage yourself. A guardian primarily deals with the health care and lifestyle needs of the person. A legally appointed guardian can decide what treatments a person receives, what surgery they can undertake, any dental needs, or whether they should be in a nursing home.
Generally medical practitioners will be obliged to liaise with and accept instructions from the guardian. You can appoint more than one guardian.