@Tamerlane Given that Alien-Chan looks almost human except for her antennae, my headcanon is that she's likely a human-hybrid made by the offscreen aliens to invade Earth (compare the Na'vi avatars in well...Avatar) in theory, stealthily. Thus, if she's biologically 99% human, that removes most of the biochemical barriers handily.
Plus, our bro is a Science Dude. Says right there on his shirt. He could probably use his FOR SCIENCE! powers with his new waifu to ensure a healthy daughteru would result from their...private research sessions.