My guess is that if they are best friends, they'll just consider the record and poster both to be both of theirs. They won't want to separate the two. And I think that they would love to have it. Give them both the record and then give them the frame. They'll hang the poster up and be happy that they have such an awesome sibling.
5 seconds of googling
http://www.amazon.com/Record-Sleeve-Display-Featuring-Plastic/dp/B009D3D3M2
http://www.amazon.com/ClassyWraps-Frame-Collection-LP-BLK-Black/dp/B002QGE3HM
Oh sorry buddy, I'm not the one who made this post. But here's something similar
https://www.amazon.com/ClassyWraps-Frame-Collection-LP-BLK-Black/dp/B002QGE3HM
My guess is that if they are best friends, they'll just consider the record and poster both to be both of theirs. They won't want to separate the two. And I think that they would love to have it. Give them both the record and then give them the frame. They'll hang the poster up and be happy that they have such an awesome sibling.
Also, if they don't have a turntable, [LP frames] (http://www.amazon.com/ClassyWraps-Frame-Collection-LP-BLK-Black/dp/B002QGE3HM) are pretty cheap and would allow them to display the LP, too. Just tell them to keep them away from direct sunlight, or the picture will fade.