Hello Pumpkin
After reading your replies a few times, I have a few observations.
It is maybe a hopeful dream of your twin to think that his world would be, or would have been better if he'd been born a girl. Honestly, this is unprovable, and leads nowhere useful. But it is in line with someone trying to run away from their present life.
Flipping to the other side, the fact that he's big and tall is not an impediment to transitioning and living as a woman. But it does require immense courage and a thick skin, and the women on this site who have similar situations have come to terms with it, and have my immense admiration. (See Pikachu's thread this week on height - it is informative!)
If he's looking for a relationship, this is another question. Many of us (that means me

) get married partly in the hope that it will cure us, or at least distract us enough to permit us to function more or less normally. Sometimes it works.
The picture you are painting is of a person who could benefit by clarifying his mind. This means therapy. Some people consider therapy to mean that you're nuts, but the reality is far from this. As a matter of formal process all transgender people in civilised countries are obliged to undergo therapy, as part of transition but many of us started it long before, as a way to understand and cope with our frequently complex minds. The result of the therapy may be a formal diagnosis of gender dysphoria, or it may simply provide the person with coping mechanism for day-to-day living. But if therapy is taken seriously it provides a mass of personal growth and insight.
I wanted to return to the point of things being easier for your twin as a girl, or if he'd been you and completed college. Maybe they might be, but without exception all my girlfriends and many work colleagues talk about male privilege they've had to overcome. I am starting to see this myself, but am fighting it. For most of us it's s price we pay, albeit grudgingly.
The dynamic you have with your twin sounds quite complex. Perhaps to the extent that some joint therapy may be good for both of you.
No panaceas here, but plenty of signposts...
Julia