How do I get conservatorship of my elderly father

My father is 81 years old. His health has been failing. I have power of attorney over my dad's finances. My son and his wife are cutting me out of his like telling me they will give me stubs to have me pay. I told them to leave his billing address at my house. They've been changing it anyay. I've had to call the doctors, give them my power of attorney and have it changed back. My daughter in law told me that my son told her to not let me know anything that's going on medically with my dad. I told her that was not ok. I will only pay bills that come to my house. I am being shut out of my dad's life. I don't know what to do. My dad has had a stroke and has memory loss. I have a doctor statement stating so. What do I do?