Elderly parents both 99

Morning I am finding things very difficult at the moment. I have two elderly parents both aged 99. A couple of weeks ago my DD was taken into hospital as he had a lung infection he’s also got Alzheimer’s. They have both constantly refused any outside help apart from myself and my sister. Last year my DH was diagnosed with a serious blood condition and was very ill. I looked after him and due to being v tired I too took I’ll. I was therefore unable to do quite as much for my parents. During my Dd stay in hospital I have visited whenever I could my sister has let it be known that I have done nothing for years a blatant lie. In fact I brought my mother to stay with me last week during that time my DH took I’ll and I had to ask for a drs visit. My sister has family and gets help via her grown up daughter and son. I don’t have anyone apart from my DH n don’t live quite so near. My son works in the Far East and my Daughter works in Dubai. My sister has never given me her mobile number in case I need to contact her. She never calls me not even when I was in hospital myself recently nor do any of her family. She sent a text to my daughter claiming I had done nothing. This is so untrue I have done numerous hospital visits cooked meals n done shopping. In fact my parents GP realised the situation after my mother fell n wanted then to have some care. I went through everything with a Social worker n my mother agreed to help for a few hours once per week. I thought at least it was a start. All was ready to commence when the social worker called to say my sister had phoned her and she had discussed with my mother and that no help was required. I just don’t know what more I can do. My DH is 78 and not a well man. My mother demands to be taken to see my DD in hospital each evening. I cannot do this as much as my sister with help from her family. I took my mother home two days ago and had to ask my son daughter to text her as I won’t be given her mobile number. My daughter did that for me. During my mothers stay with me not one call cane from my sister to see how she was. I believe she is staying over now at my mothers but leaves her on her own all day. It’s a dreadful situation and don’t know what to do