My parents treat all of us the same.
DPs mother treats her 3 children very differently. At half terms etc she will always help out with sil or bils children. For example when dp asked last week if she'd like to see her gcs over this half term she said sorry full up with sil and bils kids.
Last half term he asked weeks in advance and she said 'sorry waiting to see whether I'm having bil and sils kids, because you know they always come and stay with granny in the holidays and I don't want to disappoint them'.
I have been with dp 15 years now and there is nothing I can do to change this woman. Its like we don't even matter. They come and stay with bil (15 miles from us) once a month but never even let us know they are coming down, and they visit sil (10 miles from us in other direction) every time they are down but don't call in on us and we live in between sil and bil!
I agree with poster above who said mil is a bully. Mine is too. After 10 years I thougth things were getting better between us but then she booked a holiday cottage, invited dp and the kids and said there was no room for me. Since then things have been civil on my part, with her STILL telling everyone how rude and cold I am.
Two things to remember though (I have sons and beleive in Karma). You canl learn from this how NOT to behave when you are a mil. and, she is is dps mother and the grandmother of my children. I can't interfere with that relationship, so when they visit I am civil, and I would never stop them from seeing the kids or have any fall-out with her which would make things difficult for dp.
It does help that he gets just as upset over it as I do - he says 'its them thats missing out on these lovely kids' and he is right.
Its shit isn't it? You grow up in a nice family where everyone is treated equally then fate catapults you into a family with 'favourites' and its no wonder we don't know how to deal with it.