visiting my brother who has gardian

i want to ask about the laws in USA about this issue i have with my sister husband who lives in USA.very briefly my sister was the legal guardian on my brother who was shot in 1985 and he got mental disability since that time ,now my sister has a disease Alzheimer advanced stage which i did not know about until my mothers death in feb.2015 , and now her husband is her legal guardian and i am not sure if on my brother too. what happened after my mom death, is that we asked my sister husband about the death certificate for my mom and he refused to talk to us and even he did not inform us about her death,so i asked nancey to call him asking about the death certificate and he refused too.i contacted the funeral home and asked them about my mothers death certificate, i talked to the person who responsible for that and asked for a copy he said that they don't have a copy because my brother in law took all the papers and even the copies and that they cant help me. again i talked to my brother in law that i am coming to usa to visit my sister and my brother and i was disappointed that he didn't want, and started to give excuses that hes busy and he said ill put you on my lest next year , i asked about my brothers address or his phone he said i don't give his phone or even any information about him ,and hes going to trans fare him to another rehabilitation center and hes busy and he wanted to end the call and i said ok no problem .i think hes his legal guardian from the way he was talking to me and i know why hes behaving like that.