Grandparents favor certain grandkids

Ok so I'm not sure how to handle this or should i step back or what. I have 2 siblings one bro one sis both have kids and I'm the youngest. My sisters kids are all grown and pretty well moved away(17yr age difference between her and i not to mention she lives a country away).

My brother on the other hand (9yrs older) had kids after me. I was a single mom lived with my parent first 4 yrs of my sons life and he often goes over to see them now that we've moved. They have always been my support and backup.

Now My brother and his wife are in a different pay bracket, well to do, big house, influential friends basically they see us as rather plebian(didnt know this till recently). Parents Small plot of land older trailer and i have a itty bitty cute 3 bedroom cottage on 3/4 an acre in the sticks!

For the past 3 years none of us have been invited to there birthday parties and rarely there family function. They are always invited to ours(new years, xmas, thanksgiving, halloween, labor day, 4th juky, easter, about 4-5others a year!). Usually the only time we see them though is maybe christmas and sometimes with easter or 4th of july. We see they invite her mom to baseball games, social events, ballet recitals, family gatherings, etc via facebook pictures and we have NEVER said a thing there life there choice. My mother has been invited 1x to a football game and that was it. And i know my mom doesn't stomp on boundaries she is fine with anything they chose to do with there kids now her mom on the other hand got in a huge sulk and was rude as hell at xmas when my SIL gave her son a 2nd piece of bread since "he'll get fat!" He was 3 his first bday she got mad that we got him a toy that wasnt approved by some association at hus 3rd and last party we were at my mom got him the same gift her mom got him and man it PISSED her off!

So in turn i have tried to compensate i always involved my mom in her grandsons life, school events, helping with bday parties, christmas, he stays over about every 2nd to 3rd weekend etc. And my mom does she dotes on him, as she does her other grandkids when they come around.

Now here to the consternation i am pregnant with my second and married due in a month. My mom is ecstatic and we have had fun this pregnancy. My nephews bday rolled around no invitation, no mention of a party, nothing. So my babyshower ends up being the weekend after his bday.....low and behold i get a nasty text about how its not enough grandma dotes only on 1 grandkid but i have to steal there sons special time too? I finally messaged back and said we didn't know there was a party this weekend we never do and that we have already sent a gift just in case. And that if they want anyone to be more involved then a phone works 2 ways as she can see.

I never got a reply but my mom sure did and was in tears just heartbroken. I read the text and they were cruel. From blame for not being more involved to sly little comments about not having as much money as them to point blank saying there home isnt safe for them to babysit. They even told her its her fault that she's an enabler and the reason one of the other grandkids got into drugs.

I've already cut them off, i wish my mom would do the same but she got an invite to the party and i told her GO hell my baby shower will be attended by our entire famiy itll be fine she has already done so much for me but i can tell she is so torn!

But how do i handle this or should i just step back? I want to call my brother and SIL and fucking cuss them out for stressing a 68yr old woman! And spouting bullshit!

What would you do?