How do I deal with my sister?

Hi, I need some advice. I have an older sister who is 20 months older. As far as I can remember, she has been self oriented and sought a lot of attention. My mother always accomodated her needs and gve her the attention that she wanted. There were some sibling rivalry between us, but eventually I passed that mark as I got older.

Now we are in mid-30s and I and my partner are professionals (with designations). She has been married for 7 years and has two boys. Her relationship with her partner is somewhat strange to the social norm as her husband is controlling and she is submissive. The problem is that she uses my parents for domestic help whenever they come for visit. We are from an Asian country and my parents don’t speak English. Everytime they come, my mother works 24/7 to cook, clean and babysit. My mother is a retired teacher and my dad is retired and not well (lung capacity is 1/7 of a normal person). My mother has to care for my sick father and almost works like a maid for my sister.

During the last visit, my mother got so upset and almost had an anxiety attack. The thing is my mother doesn’t speak up because she is so worried about my sister’s marriage. Since 3 years ago, she stopped working (due to relocation) and has been a stayhome mom who doesn’t do much chores. Her husband works a lot of hours and cooks/cleans, etc. Therefore, my mother wants to pick up the slack to somehow cheer up my bro-in law (although she is not the wife). My sister is currently studying in hopes to become an accountant, which seems somewhat unrealistic (I am not trying to be mean but I and my partner are both accountants so we know what is required). She studied more than 5 years to finish an accounting program before she had kids but never finished. She also has poor language skills, which will make it even more defficult.

The issue is that my parents are coming back in late April and will stay at my sister’s house for a couple of months. I am so tired of hearing and seeing my mother at an unspeakable state and I don’t think it is fair for her. However, my mother is not likely to stand up for herself. I don’t want to be any savior or anything but I feel very annoyed and somewhat upset at how my sister treats my parents. She has been the source of problem for the family for a long time and caused quite a disturbance to my parents in her 20’s. I have written her off so many times in life so far but it is hard to keep the distance from her because she is the only blood relative in the country (my parents and brother are still back home)

I feel she keeps her two boys as hostages because my parents want to see their grandkids and in exchange for that, my mother has to work for my sister. There seems to be some problem with my sister’s relationship with her husband and that is why my mother feels pressured to work even harder to make my bro-in law’s life little easier (i.e. clean house, dinner prepared, etc). I am not sure what do any more because everytime I write off, I end up right back to Sq. 1 My mother always asked me to give in/provide for my sister and that kind of made me grow up. Frankly speaking, my sister doesn’t really enjoy motherhood and blaimed my mother for her having children (mom, you asked for it!), which made me laugh. She also acted as if she was doing a favor for the family when she was preg. (as it was the first grandkid).

How do you deal with a person like this? I just want my parents to enjoy their retirement and they have done their job raising us so it is not my mom’s responsibiltiy to take care of the grandkids. I am just so tired of her and feel really ashamed to say I am related to her. The matuirty is not there and I don’t come across people like this in my social circles. I think that she is very insecure in many ways so that makes it very hard to communicate with her; however, she doesn’t do anything positive to improve herself/situation. I don’t think I can give in/accomodate any more. I feel that she thinks she is the main character in the movie and everyone else has supporting roles. I wish she were born in a royal family! I feel that she is still like 16 Any advice???