Hi, I'd like to help you with your question.
It sounds like you want to see your sisters more often and be closer to them. Maybe you had an idea of what you thought moving back home would be like and no one in the family has done what you thought they would do. It is understandable that you would feel upset, especially when you are trying to connect with them and they are not trying to connect with you.
Could it be that they are too busy? Maybe the times they are coming over are the best time they have available to be there. Visiting takes a while, so they may just want to be there when they feel they can spend enough time and not just run in and out.
Do your sisters have other family obligations? They may feel pulled to be in many places and are stressed.
Maybe seeing your mom struggling with dementia makes them sad or upset. It could be difficult. And if your mom has any other illnesses that could affect how they feel as well.
Have you tried talking with your sisters about how you feel? It may be worth trying to get together and talking about it. If you choose to do so, be sure to present your feelings with "I" statements. Leave out blaming or any other accusing types of words. Just let them know you would enjoy seeing them more often outside of your home. Start by asking if they would be able to see you once a month for a movie or dinner. Keep it simple and fun. Be flexible. Hopefully, they will be willing to try.
You can also try attending special events with them. A concert, art show, things like that. Maybe if you all could share an interest or experience, it would make you feel closer.
Also, keep yourself busy. You do work and you have your mother so that is a lot. But don't forget to develop outside interests. Take a class, join a group, or take regular walks in the park. Whatever can get you out and meeting people. You need ways to alleviate some of the stress of your job and caring for your mom.
I hope this has helped you,