I'm sorry that you have to go through this. My husband has lived this almost his entire life...his mother being single and dumping him on an Aunt a bunch until he was 7 and she remarried. The man she married (my fil) adopted him, and they had another son together, and that's when the trouble started. My husband wanted a bike....get a paper route and save, the brother wants a bike...gets it as a gift AND a scooter, then a dirt bike, and then a car and on and on. My husband not allowed to hang anything in his room, the brother's room COVERED in posters, my husband raking leaves and pulling weeds, the brother playing ball etc. Now that they are older, I thought we had it made as we gave them what the brother said he would never give them,......a grandchild. When our daughter was 5, the most selfish brother on the planet started cheating on his high school sweetheart and wife of over 10 years, divorced, became engaged and married to one of his girlfriends, declared that he still didn't want children, and then had one, and now is expecting a 2nd one! My mother in law is going up to NC a week before this next one is due to arrive, and staying for four weeks because.......oh my gosh,,,,,,she is having a planned C-section on Dec 1 and needs help with baby #1, and won't be able to grocery shop, run errands, etc....because she is the first woman EVER to have a 2nd child by c-section when the first is 2! (did I mention that they live with her mother) We live 2 hours away and they see our daughter 2-4 times a year. In 7 1/2 years......6 birthdays, 2 of 4 ballet recitals, Thanksgiving and Christmas. They can't even meet us 1/2 way for Easter Brunch someplace because she "has to do laundry". When we are at their house the obvious picture inequality is obsurd! I send school pictures, Easter pictures, Christmas pictures, Halloween pictures etc.....almost none of which are displayed, but wedding pictures, baby pictures, Christmas pictures etc are all over the place of the darling son and his darling offspring and girlfriend turned wifey. My husband BLASTED his mother about two years ago on the phone, and since then they have made attempts ...and invite us over for BBQ and swimming in the pool...but won't go 5 minutes out of their way to make an effort to see us....two hours away, but do go to NC for birthdays, wedding shower, baby showers, new baby etc.....
Good luck to you, I don't have any answers for you, but know that you are not alone!