Dear OP,
First of all congratulations on your beautiful 2 year old girl. Im sure you love her to the Moon and back and Dad is doting on her.
This is raw because its happening now with SIL and you are being retraumatised. (Im a Counselling Student by the way.)
What you experienced at the hands of your Brother and Sister in Law was trauma. Firstly the loss;
You were family, friends, social companions, they shunned you and Hubby. They shunned your beautiful new Child.
Let me be clear, Autism is a Spectrum, 1 person with ASD is 1 person with ASD, no two react the same. Empathy is not lost on Autists, no stereotypes exist.
Your Sister in Law chose to behave in a selfish, rude, jealous dismissive way to your news initially, then as time went on they stuck with those thoughts and you three as a Family were erased, it was disgraceful way to treat Family.
Life is life, there is no rule book, you didn't need to wait until SIL had her 1st baby before you! Life doesn't work like this...
As children we learn turn taking, as children we learn we are not always the winner, the 1st, the receiver of the toy or 1st on the slide or swing. This teaches us for adulthood.
As adults, its not always "our time". As adults we know we need to wait our turn, to have grace and gratitude and hope, love in our hearts and to have the patience to know "our time too will come".
Ive always lived this way and Ive had pregnancy loss and successfully have a loving beautiful Boy who has ABI (acquired brain injury) Non Verbal with complex medical needs.
I have been treated as you have announcing pregnancy. I too made time to personally reach the intended to "gently" break my Pregnancy to her, she chose to shout out loud at me and run from me crying in a Shopping Mall having coffee, ledt me sat on my own.
Time has moved on and this Lady still has the same issues whether it be me booking a holiday, having a Wedding Album (as they did!) getting a rug, new jewellery, a Birthday Party, haircut, aquiring a Car etc etc yet I don't expect her praise or reaction, I am happy with my achievements and I thank God (Im a Christian) for my blessings and I continue to be myself, which includes letting her show me her successes and gains. I am complimentary and super excited for People, I am a lover of People doing well and I accept that its not always my turn. I won't let someone elses reactions change me as a person.
It is extremely hurtful that your beautiful child was ignored and was side stepped whilst others chose not to join in the beauty & blessing that is a new baby arriving.
She also had trauma, the baby loss is brutal I know this.
Though not everyone will act as she did.
I didn't, in fact I remember it was my friend with her new baby whom I invited to mine for a little baby shower who cried her eyes out when I told her I had miscarried.
I was coping on my own way and I was happy for her and so delighted her wee Boy had a brand new Sister.
She is still a best friend.
Life is Life, no rules no laws in births and deaths its all unknown.
Initial reactions sometimes are knee jerks, yet to have time pass and they chose to null and void you for two and half years and your beautiful daughter too, its not acceptable behaviour.
It really will be you and your Hubby who on acknowledging the birth of their child (you can do so with a card and a gift and you do not have to rush to do so) how close you get to their Family.
Your BIL essentially dropped his own Brother and his first born, to me its unthinkable. Jealousy did that. A little person here was innocent and their life was completely null and void to them, its a huge deal.
Treat others as you see fit. They did the unthinkable to you and you owe nothing to them, yet I know you will acknowledge the baby and do the right thing as you experienced how hurtful that was and we don't retaliate, the new child is innocent and a beautiful blessing.
Family occasions you can meet, pass yourselves, be polite, as you said this will never be what it once was and thats ok.
When People Show you who they are you need not ask them twice.
Your immediately circle is your most important Family from now and forever.
All your feelings are valid and Im so very sorry you were treated this way. No matter what, Shine your light so that others may see it and find their way.
Were not hising your daughter under a bushell, she is here, she was born into this world to shine, grow, flourish, The Adults who didn't support this were entirely wrong and she shouldn't have suffered a poor reception into The Family.
People should be evolved enough to know its not always their turn.
Hugs from Ireland.
K.