Still reeling — is this normal?

My story is stranger than fiction, and I could use some wisdom. I'm a 50yo woman, with a 60yo (sociopathic) half-brother (let's call him S) with whom I no longer associate (but that's another story). I found out recently that my 81yo mother (let's call her M) had given birth 57 years ago to another boy but gave him up for adoption. The boy (let's call him F) was adopted before he turned a year old and brought up as an only child. His birth certificate showed my mother's last name, W. Somehow, through someone else's help on Ancestry.com, he located the W family and contacted my cousin (let's call her J), who then contacted my mother. Mom initially couldn't figure out how F was related, but knew he was since he looked so much like her other son S. Eventually the memories of that stressful event unlocked, and she realized/remembered that F was her son, whom she had given up for adoption 57 years ago. The reason those memories were blocked was that the child was the result of rape by her sister's husband (let's call him B) after her sister had just given birth to their fourth child. Mom told me she had to have surgery to repair the damage that B had done. The fact that my mom has kept these memories locked away is testament to how painful they were. B also ended up molesting his three daughters, and me as well. Thankfully, he died a slow and agonizing death, but that's also another story. I'm trying to keep this in perspective, and focusing on what a wild ride this is for my mom and for F, who went from being an only (adopted) child, to having SEVEN half-siblings—me, my half brother S, my cousin J and her three siblings, and another half-sibling from B's second marriage. My mom asked me not to mention this to anyone yet. I'm trying not to freak out, but DAMN, I need some help processing all this! The issues I'm having the most trouble with… 1. My cousins are now my half-sibling's half-siblings—is that even a thing? 2. I'm sure my mom is ashamed; she doesn't want any of this added to Ancestry.com, but most of both families (M's and F's) already know. Our family tree just had branches fused together—it was screwy before, now it's just downright confusing. 3. Mom & I are looking forward to meeting F, but his father B was the bane of my existence as a child, and my hatred of B continued well into adulthood. I know my cousin J still somehow has fond memories of her father B. I wouldn't want someone to tell me my birth father was evil incarnate, so do I just avoid the subject altogether? 4. We've decided not to tell my other half-brother S about F. Yet anyway. That's just asking for more issues. Should I feel guilty? 5. My emotions have been ranging from empathy (for what my mom and F must be feeling), to outrage (at B's rape of my mom), to joy (that maybe this half-brother will be a good person), to fear (what if he's not a good person). I'm reeling! How should I be feeling? Is any of this normal? —Reeling