If a person has named her next of kin as her sister but there are estranged adult children?

I have recently lost my dear aunt, 7 years ago she lived near her adult children but was estranged from them , for many years she had not been contacted by them not allowed to see her grand children, eventually my aunt moved to Birmingham to be near her sister (my mom) and other family, my aint led a very sad life and her heart was broken by her children, now she has left us, she left no will and of course we want to ensure that her wishes are granted, my aunt wanted nothing to do with her children, in 7 years they did not visit, send a card or contact her in any way, she is not even cold yet and already her children are asking for the keys to her house, my mother is down as her next of kin at her doctors and hospital, my question is ..... is my mother her next of kin and would this be enough to prevent her children getting her estate, we do not wany my aunts money, its not about the money its the principle, my aunt would not want them even entering her home let alone getting her estate, we are finding the whole matter so distressing and it maked us physicaly sick, they are like vultures, can anyone please give me some advice.