First, you need to know if the person for whom you intend to provide care can legally sign a power of attorney. It is always better if there is some timely planning and there is no question of capacity when the powers of attorney are signed. Often though, no thought is given to the issue until the person needing care is on the brink, or over the brink, of capacity. If the person does not have capacity, you must consider going to court for a conservator or guardian.
The standards for capacity vary by state, so seek local legal advice.
If there is capacity, choose the right people
Powers of attorney are powerful instruments. They can do a lot of good in the right hands and a lot of harm in the wrong hands. Do not choose the attorney in fact, the power holder, unless that person can be trusted absolutely. Ask your attorney to provide for periodic reviews by a third party.
You want a person who is good at business and finance for the durable power of attorney. You want someone who will make the right choices with the health care power. Back up the health care power of attorney with a living will setting out end of life choices.
Know when to go to court
Properly written powers of attorney survive incapacity of the principal. So, if Mom or Dad made you a power of attorney and becomes incapacitated, you can still help them. Problems come with someone on the brink of incapacity - someone fine one day and not there the next day. A person like that can revoke the power of attorney. Then you have to go to court to continue helping.
Or, a person might clearly lack capacity, but loudly proclaim they do not like what the attorney in fact is doing. Again, you may have to go to court. As long as you are in court, you might as well seek a conservator or guardian.