'Pressured circumstances'?!
No, it would never have worked because new partner - now thankfully hopefully ex partner - is clearly an abusive immature dickhead!
I am so glad the result is this way, as if the baby had have been this twat's child, you would have been stuck with him in your life.
Your parents are also acting unforgiveably.
I suggest you tell your parents that right now, they're on the cusp of proving to you that they're not fit grandparents anyway so will soon be seeing neither you, your new baby OR your elder child. How despicable.
If you don't want to have an abortion, do not have one.
I have to say - regardless of who wants what (all these fucking people who are NOT PREGNANT wanting this and that get NO SAY) - this is not such a terrible situation.
You already have a child with this man. Not a lot really changes in a way. If you want(ed) a sibling for your older child, then this is honestly probably the best way of having that! No complicating factor of another father/family in the mix. They will be full siblings.
Your ex? Well if he didn't want another child then he shouldn't have had sex, should he? That was HIS decision made. The end.
Roast your parents and put the fear of god into them that if they EVER try and presume they do anything except respect your decision as an adult on something so personal, they'll be out of your lives.
Roast your ex and tell him his decision point on this was made long ago.
Then make your own decision. Personally, I think it is obvious you should keep a baby who is a full sibling to your older child and a baby which you want to keep!
By the way - your parents would come around. Do not make such a life changing decision on theirs, or anyone else's say so.