Wow, big hugs to you, dear one! I feel such compassin for your situation! That is a huge load of guilt that your aunt and mother are passing on to you that you do not deserve. It is not your fault! Not the childhood sexual abuse, and certainly not your traumatic birth. And for anyone to dare tell you that in addition to the pain you sufferred you were also to blame for your mom's feelings? That is just a wrong concept to put on someone. It sounds like your aunt and mom are choosing to put blame on you for some of their pain which is really not right for them to do to a child- but very likely they are not even aware they are doing it, as they are probably acting from a place of pain and feelin somewhat broken too.
The way to end the cycle is to emotionally step into your own self loving space and create a clear distinction in your mind about what your aunt and mom feel and what is true- and what you feel. So when they tell you that you hurt your mom more than you hrt yourself- ideally you could see them as a hurt inner child lashing out at you, and perhaps feel compassion. But know that they are telling their own story.
Then, if you can- start now to create a shield of sorts around you of only loving people and loving feelings, especially stemming from you to yourself! Like a little island of love (in your thoughts/mind) that is free of the criticism from anyone- even your mom and yourslef. Criticism from a parent is so hard for everyone because of how important our parents are to us.
I wuold say try to just find a way to seperate yourself from anyone else's judgement, forgive yourself for everything- wipe your slate clean and start from here internally. If you believe in God then call on God to fill you with strength and love. If you don't then find whatever it is that gives you a sens of being cared for and loved unconditionally- perhaps from your spouse or any friends who really accept you.
And then choose only people who allow you to feel safe- and who will not have any guilt or drama to lay on you- to attend your birth. A doula is a great idea. And even if you won't know the exact doctor, just having one or two people you trust around you will help a lot.
I think if you can find a place away from that burden they are rying to hand you- if you can say to your aunt (perhaps silently in your head) "no thanks, I refuse your guilt story, take it somewhere else", that would feel good.
And then tell your mom whenever you feel right about it. If you need to hold it private for now it sounds like you need to protect it- then do that.
Tell when you want to. Best of luck!