Hi @Cats101
Firstly, you are such a lovely human being. Some children are blind to the fact that their parents can experience illness and, like most of the population, require care. This is certainly not the case with you, noting your thoughtful consideration for your parents, and a need for calm in the household.
Having said that, self-care is also important, specifically, when you are carrying the bulk of responsibility for keeping things in order, including the wellbeing of your parents. To this point, and appreciating the stressors of your current living arrangements, please remember to prioritise some of the things that make you happy (its perfectly okay to put your own interests first, sometimes).
Beyond this consideration, I wonder have you ever had the opportunity to raise your concerns with your sister. This could happen over a nice cup of tea or coffee and when the anxiety you are currently experiencing has subsided. Also, have you explored the possibility of obtaining outside support (e.g., to help with cleaning, mowing, general maintenance) or to help manage your parents illness?
Lastly, please know that you are doing your best and importantly, have 'been there' for your parents in their time of need. This highlights values of love, compassion, and respect, and suggests that you have the coping skills and resilience to calmly and systematically work through your current challenges.