Jay asked for drabbles featuring Elladan and Elrohir (and anyone else the author might wish to include). This isn't a drabble, but it does feature the twins.
The sound of revelry faded as three figures slipped from the hall and out onto a secluded terrace, leaving the wedding guests behind for a time. Two of them drew the third to a halt.
The twins stood expectantly by, so Aragorn, familiar with their ways and thus on his guard, glanced round surreptitiously to make certain they were in no danger of being overseen, then opened the box and gazed within. After a moment of nonplussed staring, he said, "Please tell me you did not tell anyone you were buying this for me."
"Estel," Elladan chided, a wounded look upon his face, "we would never be so... crass!"
"You are marrying our sister, after all," Elrohir replied.
"Besides," Elladan put in, "it is customary for the bride's family to give gifts, and 'tis better to give such things from the heart and the hands, as they say."
Aragorn closed his eyes. "You made this?"
"It was mostly Elladan," Elrohir demurred. "He was more in your company on the way back from Cormallen, and so had more of a chance to observe—"
"Elrohir did the decorative bit just there—" Elladan began to point it out.
"Yes, thank you," Aragorn replied and shut the box firmly.
The twins gave each other knowing, mournful looks. "I told you, he wouldn't like it," Elrohir said.
"Estel, lad," Elladan said, draping a companionable arm around his brother-in-law's shoulders, "give us a hearing, I beg you."
"No, a moment! Arwen is our sister. Our younger sister," he said earnestly. "Now, you must admit, we have been uncommonly kind. Have we asked you about the years between twenty and fifty? Given what this marriage means for her, do you not think we have been paragons of patience and discretion?"
"You'll recall, we did not even come charging home to question you when we learned you were betrothed," Elrohir said.
"Without ever discussing the matter with us," Elladan added.
"And have we ever told you that we could slay you, but that Arwen loves you, and you are our brother?" Elrohir demanded.
"Does that count?" Aragorn asked.
"Not at all," Elrohir said, emphatically.
"Our point, Estel," Elladan said, quickly, "is that we have restrained all such impulses, though we might have vented them freely. And we have done so because we care for you, but we wish above all that Arwen be happy in her choice. And I think she would not be happy were we at odds with you, especially if on her behalf, as might be said."
"So forgive us this one jest, and keep our concern instead," Elrohir concluded, and indicated the box. "Use it or not, as it please you both, but make her happy."
"In all ways," Elladan finished, and gave him a smile. "Will you promise us that?"
Aragorn looked from one to the other, feeling suspicious wariness beginning to founder in the face of what seemed sincerity. And it was not as if he had any desire to deny them that promise. So: "Gladly, and with all my heart," he replied.
"Thank you, Brother," Elladan said, releasing him then. And they began walking back towards the hall and the celebration.
Just ere they rejoined the company, however, Elrohir touched his arm and halted him.
"I do feel, however, that as her brother, I have to warn you," he said, and looked Aragorn straight in the eye. "I do not know what experience you may have—and again, I am not asking!—but know this: whatever it is, it won't be enough to get you through the night."
"Elves, you know," Elladan chimed in by way of explanation, and smiled; "If she can imagine it clearly, she can do it."
"And Arwen is—"
"—very imaginative. Always has been. And she's had what, thirty, almost forty years to dream?"
"So you may want that after all."
"Good night, Brother! Good luck!" With that, the twins, grinning contentedly, abandoned him and returned to the hall, leaving Aragorn to collect himself—not the easiest task, given that parting jab. He glanced down at the box in his hand, and at last shook his head. There was really only one proper response to that kind of provocation...
"Bait taken," Elladan said but a little while later, watching as Aragorn whispered into Arwen's ear.
"I should think so," Elrohir replied, sipping his wine. Then: "So. Think you she will ever see what's in the box?"
"Mmmm... no, I think not," Elladan said after a moment's thought, and smiled evilly. "After all that, I imagine he will be willing to let her have her way with him, just to avoid it."
"As if it would be otherwise!"
"Indeed." Elladan raised his glass to the departing King and Queen of Gondor. "Good night, little sister—numbered as they are, may all your nights be wakeful as this one!"