Responses

The twins weren't mentioned in Romantic Joutou, but in this manga (Ai to Makoto), the alpha from Romantic Joutou was seen at the end credits of ch 7. The twins called him "Ekihito Niichan!"
It wasn't clear whether they called him "nii-chan" as a blood-related brother or simply as an older acquaintance, but there is a high possibility that they are somewhat related since they met him as they were visiting the main house.
Here's the link:
http://www.mangago.zone/read-manga/ai_to_makoto_moriyo/uu/ai_to_makoto_moriyo-chapter-7/57/
I just finished reading Romantic Joutou and decided to reread this, and omg, I'm surprised that the twins were related to that scum(?) alpha. What a small world it is xD