Am I being childish?

My mother lives with my 36 year old sister and for the past few months my sister and I have not been talking or seeing each other at all. My sister has some 'issues', basically she is very immature and angry and has never left home and only held a few jobs for a few months all up. It came to a head as I was getting annoyed with her childish nasty behaviour and we had an argument and haven't talked since. I have asked her a few times if she would like to work something out so we can get along for the sake of peace but she is not interested. (She has a history of holding grudges, and has taken turns not talking to everyone in the family for up to 2 years). Anyway my mother is playing the 'I don't want to be caught in the middle' card constantly, which is getting old because she panders to my ridiculous sister and I am not able to go around to her house while my sister is there because she wants to 'keep the peace'. (I have a toddler and baby who do like to visit). My mum and I usually go to markets on Sundays to get produce, and I cannot go this sunday because my sister wants to go. Am I childish for getting really irritated by this?? My mum is annoying me too by what seems to me to be perpetuating the problem by giving merit to my sister's stupidity. I feel like because my sister is so emotionally stunted and unable to interact properly with others, that mum needs to help her sort herself out rather than just meekly accepting all her crap. What do others think??

Have you explained to your mum how you feel about it?

I don't blame you for trying to nock some reality into your sisters brain, even I would be annoyed about it & feel the same. However; despite the differences yous have towards eachother you shouldn't have to stay away just cause your sister wants to go to. You be the wiser person & swallow your pride & go with.. There's probably a reason to why she is the way she is, you being her sister it's best that you talk to her & try & help her overcome whatever is stopping her to interact with others. As for your mother, If she feels you are right & wants her to gain some independence then she also needs to stand by you & encourage your sister to do something with her life. It could be the fact that your mother still mothers your sister OR your mother is afraid to confront your sister cause of her anger.

You're correct, your mother needs to control the situation like a mature adult. Although she states she doesn't want to get in the middle of it, she already is because if she prevents you from going there when your sister is there, then your mother has basically made a conscious decision to be in the middle of it. You, on the other hand, recognise your sister's shortcomings and immaturity and therefore you need to live your life to your standards without her negativeness. If you have tried to negotiate with your sister and it's failed, then there's no more you can do but to accept the situation. If you achieve this, you won't be irritated. Nobody can help your sister unless she recognises her own issues and then seeks help to overcome them. You have 2 children and they need you to be healthy and happy. This whole situation is unfair but while you have no support from your mother when it comes to your sister and her behavior, you are really just damaging yourself trying to resolve it.

Thanks so much for your wise replies, yes I believe my sister has mental issues, she doesn't work, or have any friends or partner apart from my mum and dad. I feel my mother is too afraid to confront my sister plus she likes to have her help around the house, as my sister does all the cooking and my mum can't cook. It frustrates me because I know this is not in my sisters best interests but she refuses to acknowledge that she has issues and would never get any help. One of the main reasons she and I are not talking is because I recently got some professional help for anxiety and she was very mean about it and repeatedly called me crazy. So she is very negative about acknowledging problems and seeking help. Thank you all so much for your replies, unbiased points of view are really helpful.