I am listed first on mom's POA and Health Care Directive and my sisters listed as second and third on forms. They live a distance away and do not know anything about mom's situation (financial, health, etc.). Since my son helps with his grandma's health situation (ambulance, hospital, doctor appointments, etc) I would like for him to have health care proxy as a back-up to me. Grandma wants it, too. Am I allowed to get that set up for him? Sisters say "no". He is always here and helping with Grandma.
I just noticed on your profile that your Mom has Alzheimer's/Dementia. Would she under the contents of a Power of Attorney? If yes, take her to an Elder Law Attorney and let her make the changes.
I recently inquired about doing a similar setup for our older brother. He was not local back in 2006 when we originally set up all the DPOA, Health Care Proxy, medical directives, etc, so he was not listed as DPOA. The elder attorney said no, we cannot "assign" a new DPOA, et al, only mom can do this and since she is not competent (would not *really* understand, even if she was agreeable), then we cannot do this. It would have to go through court, which is expensive and takes time. I advised him that if anything were to happen to the two of us who are currently DPOA, he would have to go the court route (guardianship and conservatorship).
In your case, your sisters are the backup to you (if wording specifies levels of involvement - in our case I do not think one has any higher priority over the other). They *should* at least take an interest in what goes on and how, in the event that something happens to you. This is irresponsible of them NOT to be involved. At a minimum they need to understand everything. They do not have to be "hands on", but they should understand enough to take over should they need to.