Mommy issues (not baby related)

So I need some advice on how to approach an issue w my mom. My whole life my younger (and only sibling) my brother has been able to get away with things that i could never... my mom always seemed to favor him...

Now we both have kids. He has 3 i have 3. However my mom pays for his kids (all 3) dance classes, costumes, etc. She also watches them over the weekends to help my brother and sister in law out whwn they have date nights and weekends away or if she wants to do a yoga trip or him a ju jitsu tournament. However when i ask to have her watch the kids for ANY length of time albeit mostly only hours so we can get away for a bit for dinner or just some alone time she says how busy she is. When it comes to my brother its basically she drops the world. I have approached her about it several times and nothing has changed. She says shes busy and has to work all the time. The thing that makes me mad the most is she sits up on IG and FB posting about how she loves "all 6" grandkids but all her posts are about my brothers kids. My husband wants to confront her but again its pointless. I dont know how else to address it with her. She says its because my kids require more attention and they dont behave (my 4 yr old is autistic and my 2 yr old is getting tested now too but has sensory issues). She says they cant do their own thing so she doesnt want to watch them. She didnt watch my brothers kids til one wasnt "an asshole" anymore... her words not mine..plus she wont take my step daughter out to do things w her but takes my brothers daughter out all the time. It makes me upset. She thinks throwing a few expensive gifts my way makes up for it but she only wants to be a grandma on her terms and thats not ok.

My husbands mom who has multiple health issues is over here all the time with them. She tries her damndest to help us when she can and when my mom wont.

I just dont know how to approach her about it or if i even should. Because she runs and gets my brother involved in the issue and cries poor her.. i am just sick of the fake bullshit on IG and FB and my kids suffer because of it. She wont come to my home... neither will my brother... they say its because of me but I dont know what is so wrong w me. My whole life its been my mom and my brother tight as could be and me ovee here feeling like im an afterthought. I dont care or didnt really care when it was just me but now im seeing the same shit play out between the grand kids. Any sound advice would be appreciated.