Despite feeling the need to strip him of his clothes and use him for your own pleasures, you decided to keep him as a human, for now atleast.
You gently grabbed him, "W-What are you doing?" he asked, before you took flight, hearing your human sibling scream as you flew faster, moving through clouds as you looked down, searching for a lair where you could rest and build your hoard.
While flying, you felt free, like nothing was holding you back to do whatever you wanted, unlike you parents, who constantly held you back from different things, constantly keeping you inside a room. You wanted your brother to feel the same freedom you just got, but first, you wanted to make yourself sure that he wouldn't kill you if he was transformed into a dragon, by convincing him that his parents never loved him, but you did.
After a few minutes, you found a cave, large enough for you and your sibling, and it was located near a kingdom, you didn't know much about it, except that it was ruled by a queen, who was interested in the arcane arts. You could easily fly there and decimate everything or force the queen to surrender, and command her just like a slave.
You landed, gently putting your brother on the ground, who looked at you confused, "Why didn't you kill me?" he asked, as you gently pushed him towards the cavern as you went inside, "Because you're my sibling, and unlike our parents, I love and care about you." you replied, stopping for a moment to move one of you claws towards him. On it, there was a ring, which managed to survive your painful yet pleasurable transformation, it was the only gift your father gave to you and your sibling.
He let out a gasp of suprise, 'Y-You're lying, my parents loved me and my br-" he started, being interrupted as you growled and puffed out clouds of smoke from your nostrils, "And yet they kept us locked in our chambers, blocked from the entire world, and when that dragon attacked the capital and reached the throne room, they watched it as he stripped off my clothes, before he raped me, and turned me into what I am." you stated, glancing at your body, specifically the area where your clit was, feeling the need to rub it, "And what did father do after I killed that dragon? He tried to kill me." you finished.
During that time, your human sibling listened, and when you finished he looked at you, as much as he didn't want to believe it, he understood that you are his sibling, now a dragoness.
A few minutes passed, and your human brother was asleep, near a fire created by you. Meanwhile, you laid your back on one of the walls of the cave, still exploring your body, running your hands across your scales, you felt the urge to pleasure yourself, to find a mate and to lay eggs, and to transform your sibling, you felt the need to destory the entire kingdom near your lair, and to feed.