Which is better to have POA or conservatorship?

My father was recently diagnosed with dementia and my mother whom he is married to is having a difficult time handling all his affairs. My siblings and I agree it would be beneficial to be able to take over so we can better assist in finding our father the care he needs. We would also be able to be more hands on with things in regards to his treatment/placement and medical expenses. Most times we find our hands are tied and our mother is overwhelmed at dealing with all the the capacities involved. Is she automatically given the right to make decisions for him and can she sign that over to us or would we need to go through a hearing? We are just trying to make sure all needs are met in a timely manner.