Sister-in-law of the Heroine in a Childcare Novel

I was reincarnated as a villainous side character in a childcare novel. Obsessed with and clinging to the adorable female protagonist’s eldest brother, I ended up poisoning the female protagonist and meeting my ruin as a worthless princess. I’m done with you all! That’s what I promised myself as I got ready to run away. But after I saved the female lead, everything went off the trails. “Anyone who lays a hand on Sister, I’ll hunt them to the ends of the earth and destroy them.” “The imperial family? The useless imperial family that only brings misery to Titania. Who cares what happens to them?” “Hahahaha, they call me a mad dog, but why are their heads so empty? If a mad dog only bites certain people, is it really a mad dog?” Ca-Calm down, everyone. I’m planning to leave for a seaside villa where the waves are beautiful, to enjoy a life of dreams, hope, and riches! I hope you all find happiness too! …Or so I thought. “...You. I really believed you were dead, and I...” His golden eyes, fixed on me, were awash with emotions I couldn’t read. Just looking at them made me feel like I might drown. “…It felt like I was trapped in a never-ending nightmare, Tia.” He pleaded desperately, whispering for me not to disappear from his sight ever again. I was left speechless as he gripped his hand as if to bind me, not letting me go anywhere. And then— “It’s okay if you hate my brother. It’s okay if you find my dad annoying! But please, don’t hate my family’s money!” ...The adorable female protagonist suddenly pressed the key to the underground vault, where all her family’s treasures are kept, into my hand. “Are you tired of everything? Then pick me instead of my brother. Don’t bother with being the duchess or anything like that. I’ll always be by your side, whenever and wherever. What? Don’t make a sound like a dog? Woof woof, grrr, ruff ruff!” Even the female protagonist’s second brother, who always looked at me like I was a thorn in his side, was acting strange now. What’s wrong with you all?