Daughter becoming carer for my parents

Hi,

I am new to this forum and am posting as I am struggling to deal with my elderly parent's anxiety and over-reliance ( as I see it) on me and my guilt at feeling this way. My Mum has stage 4 TNBC and has just started a new chemo regime. She was diagnosed in February 2021 and it has been a roller coaster ever since. My parents had only very recently moved to be nearer to me when Mum was diagnosed and combined with that and covid they became very reliant on me. After Mum's diagnosis I willingly did more for them than necessary and they have now become over-reliant on me as a result. My mental health and marriage are suffering as I struggle with the responsibility of supporting them and living my own life. They are both aware that their anxiety issues are making a horrible situation more difficult but neither is willing to explore getting any help. At the moment all three of us are struggling and trying to find a way forward where life is calmer is seemingly beyond us. My brother lives away and is theoretically supportive but in practical terms is not actually helping ( I am guessing this is a classic scenario where one child lives away ) and doesn't see what the problem is. I am struggling with the transition from daughter to carer that seems to be happening, and worry that they are relying on me not just for things they cannot manage but for things they would just rather not do. I am beginning to resent the time spent with them ( to my shame) as every visit is miserable and does not focus on anything else than Mum's illness and Dad's hopelessness.I have suggested a variety of things for them to think about getting some help but they are not receptive. I know that there is only so much I can do to help them with their emotional needs as well as dealing with my own , but feel guilty that I cannot help them and that I am beginning to get irritable with them. I have tried to create boundaries but they don't last .I know that things are going to get worse as Mum's health fails and want to 'save myself' for when the going really gets tough rather than spending a lot of time now on what I see as minor issues. I feel dreadful for not coping better and wanting to have more of my old life back and wonder how others have dealt with the compromise needed .