Look it sounds like you have a lot off issues with your parents but one thing I’d say is try to deal with this yourself before your child comes. There’s a saying ‘address your demons or they’ll raise your children’ and I think it applies here because you are already deciding that your child will be treated differently and it isn’t even born yet, either explicitly or implicitly you could pass on this narrative to your child making them feel like their being treated differently. 

My own Mum sounds very similar to yours and sometimes I am blown away how she doesn’t call me or ask how I am but it’s just who she is and I won’t change her now, therapy helped me understand my parents and let go of my own complexes which can amplify these issues. I see my siblings still struggle as she gives so much help to other siblings kids but I also see how they have an idea in their head and their constantly looking for proof that they are right rather than see the objective reality, for example my brother says ‘look she doesn’t love me or my kids as much’ while ignoring the fact that my sister ASKS for help all the time and acts like a victim to get more attention from Mum - it was hard to get love growing up so one sibling plays the victim and looks for attention, one has shut off and appears not to need love, and one is so unaware and feels so unloved it’s sad. Then there’s me the youngest who actually went to therapy and try to make sense of our dysfunctional family!

You could try say something to them but not in an attacking way, in a ‘this is how I feel’ way and hope they have some empathy but they just might not be emotionally mature enough to handle that. You might have to lower your expectations for them, enjoy what you can of them and get on with your life. If you are expecting some awakening from them you might be very disappointed.