The afterglow of the wishes and the sex was making both of them consider another possibility. Eileen had enjoyed fucking Ty's ass, a lot, but an instinctual part of him was taking hold- just as she had felt attraction to men as a woman, now he felt attraction to women as a man. With this body, with this penis, he could have sex with a woman, and cum inside her, and get her pregnant. And a part of him ached for Ty to make himself into a girl so Eileen could get to do it.
Likewise, Ty was contemplating what it might be like to be a girl. Changing into a guy had made Eileen feel so good, and he'd been so hot, and Ty felt like he'd like to try being a girl if nothing else. Especially because he knew he'd like to try getting tits to play with, and being fucked in a pussy instead of his ass, and maybe even... knocked up?
They looked at each other, and spoke the same wish almost in unison.
"Ty, do you wanna-"
"Eileen, what if I-"
"Turn into a girl?"