Amycus had not been looking forward to this quite as much as Lucius had. Admittedly, sex with Lucius was generally pretty great, but watching his sister have sex with someone else was not exactly something he relished. Lucius knew this, and Amycus was absolutely sure he would play up to it - that was what was fun for him. Lucius was kind of an asshole.
He held Alecto's hand as they approached the Manor. He suspected Lucius would be watching them, and would think it rather funny, but he didn't care. He needed to reassure her, and he needed to feel connected to her.
The House Elf took their outer robes, and Amycus found himself wondering just how much those creatures had seen in this house, of Lucius' exploits. Then Lucius himself arrived, and commanded all attention. Of course they weren't late, they wouldn't be late for something like this, but Amycus was ready to take the blame anyway.