I struggled whether to post or not. I am so sorry this is what you're facing and so sorry your parents aren't able to split themselves better, while also having some sympathy for them too. No one trains anyone how to cope with the unthinkable.
Your pregnancy hormones may also be doing all sorts to you, and when your child is with you, it may upset or stabilize that apple cart.
It does sound like you're suffering 'golden child' syndrome, as a result of awful tragedy and your parents over focusing. You're facing a double loss. (IMO so are they) If you can afford counseling, definitely go for it, and use it to also explore how to talk to your parents. The family dynamics sound suffocating.
The situation here is then young teen, suffered sudden severe injury and acquired brain damage. She was pretty much left to die.
It was instinctive to fight to keep her alive and give her the best possible chance, which also meant nursing her 24 hrs. A sibling was drafted in to allow any sleep. None of us thought about consequences, but of course they still happened.
I've always accepted siblings accidental pregnancy through disrupted birth control while taking turns in shifts with me, was one of the many accidental results of our disrupted lives. Another sibling furious she was sexually active!
I've done my best to split my attention and resources as best I can, but the truth is for many years, the lions share did go to their disabled sibling, or fighting legal cases for her, or SS when I finely managed to win some money for her. (Suddenly SS was interested!)
They've had to live with so much and it's all been blisteringly painful for everyone and doesn't end.
'She' has unexpectedly recovered a life against the odds. Some's luck, some a great deal of hard work. But it is such a very different, disabled, limited, slow, heavy, and self absorbed life, that's peaked now. 'She now' is so very different from their light bright funny sibling, with almost no resemblance to who or how she was, requiring 24/7 care, and life requires planning around her.
The simple reality is the vast majority of the original 'her' died that day, and from her siblings pov, all of her. But the painful reminder and slower death of her lifestyle slowing killing her, is reality now. Witnessing her dying slowly from the only lifestyle that brings her happiness, isn't easy for anyone.
But, she may outlive me. I've had it more than once, that everything is my fault.
I and they, find the 'we learn so much from the disabled' nauseating even if it has truths. Now I'm also viably disabled myself that tripe has at least ended.
So we're very different from your family set up, but all but one (has their own issues) have at various times exploded at me over the unfairness of the amount of attention she's taken up. It's been translated as me not caring enough about them, despite (apart from the first month when we all were in auto) having bent over backwards to ensure special moments, achievements, and milestones are noticed, celebrated, and praised, and being an available grandmother helping them home ed. One has also claimed I over favored sibling who got pregnant.
Yet they're all otherwise very un jealous and supportive of each other!
I think it may go with the territory to some extent, as when we've talked about it, it seems to be more about how planning round her needs, and thus she has presence in everything, made them feel somehow less important and like that original awful shocking day just never ended for them, no matter what I did.
Two of her siblings have at various times said or shouted at me, that they wished she'd died that day. Thankfully never around her. Once that they'd be glad when she'd gone. We all ended up crying over the reality. It hurts to hear, but their complicated feelings in a complicated situation are, well... complicated.
The biggest difference here is how we communicate, but even in an openly communicative family, some of the residual feelings suffered, may be simply the the cruel icing on a never-ending cruel cake.