I haven't commented on the "who should see the baby first?" issue, because it's not really of any significance when your husband treats you like your feelings about your own labour don't matter.
I think the advice for the grannies to come to the hospital and see the baby together is not great.
Far better for you, the baby, and each granny for them to come to you one at a time.
Presuming your MIL is a kind and decent woman who isn't involved in her son's awful behaviour, I would consider letting her in first, especially if she helps out by giving your mother a lift.
On that day, she will have just become a grandmother. That's a big thing in her life. I remember how excited my parents were (especially my Dad) to become grandparents. It is really special.
Your mum will love this baby just as much, but she's already a grandmother. I love all my children equally, and the arrival of the first was the least pleasant, but becoming a mother was a huge thing. That only happened once.
Also, your Mum, being your Mum, is likely to see a fair bit more of this baby in the early days. I think you could even things up a bit for his other (brand new) granny by letting her in first.
But none of this is as important as making sure you have a supportive, non-abusive birth partner.