He complies, remaining silent

The twin remains silent. He's simply shaking in place, looking at you in wide eyed terror. "Good. Now what is your name? What is your brother's?"

His voice trembles as he tries to whisper, "I-I'm Dromio. Th-th-that's muh-my bra-brath-brother, Ph-Pholus. Peh-Please don-don't kh-kill us."

You shake your head. "I'm not here to kill anyone. I was cursed to breed, so I must deposit my seed within another lest I be driven mad." Your cock twitches against the confines of your loincloth, eliciting a groan from you. "I have a proposition for you. Either offer yourself to me and spare your brother, or assist me in breeding your brother. It's your choice."

Dromio trembles as he hesitates. His eyes flicker between you and his sleeping brother. You grow impatient, yelling in whisper, "Pick now or else I'll break you both!"