Can't find any

This is a classic, though it has been almost completely removed from the net

https://web.archive.org/web/20170228004020/https://www.literotica.com/s/german-nanny-and-boyfriends-brother

Boyfriend's brother "tries her out."

I've also been reading a recent series about a loser brother "teaching" his far more successful brother's naive wife:

https://www.literotica.com/stories/memberpage.php?uid=7156742&page=submissions

And a classic, Little Brother's Huge Twisted Problem. The brother is adopted, but the favorite of mom.

https://web.archive.org/web/20160927102157/http://www.asstr.org/files/Authors/zipp2/www/Little%20Brothers%20Huge%20Twisted%20Problem.html


It's only tangentially related, but Orestes is a fabulous author and I'd hate to not give them credit. In this a man finds that his wife and her sister, along with her husband (so MC's brother-in-law), have a sort of clique to themselves that he has a hard time getting into.
https://asstr.xyz/files/Authors/Orestes/newcomer.txt

The Unwanted Houseguest is probably the most read version of it on the net, made by the incredibly prolific Stormbringer
https://www.literotica.com/s/the-unwanted-houseguest
He recently began a new version of it with some illustrations
https://www.literotica.com/s/the-unwanted-houseguest-rebooted-01

There's also these three
This author has "Bigger, Better, Brother" in three parts: https://www.literotica.com/stories/memberpage.php?uid=5858468&page=submissions
Little Brother Comes to Visit: https://www.literotica.com/s/my-little-brother-comes-to-visit
And Little Brother No More: http://mypervertedstories.com/wp/index.php/2016/10/21/little-brother-no-more/

Huge contribution, it's a shame "Little Brother’s Huge Twisted Problem" doesn't get a sequel... truly a classic.
Talking about "The Unwanted Houseguest" I remembered the Indian story "The Unwanted Houseguest". It's really good too, no mom ntr, but a excellent mystery ntr...one of the best experiences you will have reading.

Changing subject a little, I enjoy stories that the whole family is into incest except the son (MC), unfortunately there's not too much of them...Soon I will post some that I know