What are the laws on terminating a life at a hospital?

My mother was very ill, she actually had a cardiac arrest and the hospital brought her back. There are 15 siblings in my family, one has the power to pull life support, my mother was never on life support just oxygen, she was breathing on her own and talking, new what day it was and who each of us were. She was in the hospital and somehow the decision came to take her off oxygen and pump her full of drugs so she wouldn't feel it? We waited for my brother to show up and from what I was told if she didn't want to remove her mask that it was her decision after he showed up. The nurses came in after my brother showed up to switch her oxygen mask to one that would as they put it "allow her to live for 5 min. to 4 hrs". When they went to due this she told them "no" and they left the room. This all was at 1:00a.m. and there were about 12 of us there then. Me and four of my brothers and sisters stayed all night, at 5:00a.m. my sister texted me while sitting in the room that she wanted the mask off at 6:00a.m. and to see if I was alright with that knowing my mom didn't want it off and my little brother and I very much against it. I told my sister that when my little brother woke up we would all talk and see how mom was doing then and go from there. I left just before 6a.m. to get something to eat and a coffee, when I returned from the room they had just switched masks and pulled a needle from her full of pain medicine and something I can't remember, needless to say my mom was out, still breathing but doped up too much to talk. My sister told the nurses to do it while I was gone and my little brother sleeping in the room where my mother was. My mom woke up a couple of hours later and realized what was on her face (oxygen mask) and said "well I guess I'll be going soon, now" since she never told them to do this. I left the hospital to take a shower and was on my way back when I got a text from my little brother telling me that the doctors are dropping the oxygen by (1) every hour until she goes, apparently she was going to live longer than they thought so my sister again gave them the o.k. to put her down in this way without consulting the family. By the way the sister that was giving the instructions to the doctor was not the one listed in my mothers living will to make these decisions, but she is the executor of estate and will not show anyone the will and has taken stuff from my mothers house without telling anyone and is selling stuff without allowing the beneficiaries time to go through my parents personal belongings like my parents wanted. What I would like to know is, what are our rights and what laws are out there for what my sister did to my mother and is still doing to my mother? How do you stop the person who gave the o.k. to kill your mother with the istance of a hospital??? Please help me figure this out, thanks.