From Storm in Heaven:

Russia, 1828. Natalia's family is fallen nobility, left poor by her father's chronic illness and mother's poor management. Her family's only chance at revival is her marriage to a wealthy noble. With her family's hopes riding on her future husband, what chance does a poor poet have at winning her heart...?
And the "poor poet" is no other than the famous Russian poet Aleksander Pushkin.

From DramaQueen:
Momoki Asuka and Momoki Yui are two step brothers who were the best of friends until an unfortunate incident one summer's day. Ever since then, Yui has avoided Asuka at all costs, even going so far as America to study.

A super tennis star, Yui no longer needs a big brother, so where does that leave poor Asuka? What happens when brotherly love transforms into something more?

Volume 1 - Brother
Volume 2 - Brother 2

From Nakama:

Hikaru and Chikage, twins who grew up in an orphanage, are taken into the home of Yukihito-san, a doctor who has been taking care of them. When they nervously open the door to the Ishiki household, what's there is... a garden of beautiful brothers. Their new family has eleven gorgeous brothers who are renowned throughout the neighborhood. Surrounded by a kind and perverted family, what will be the fate of the twins? Each day is a chastity survival game!

Kondo Masahito is a tough high school senior, while his older brother Yoshio is a calm and gentle kindergarten teacher, so it is not rare that younger brother protects the older one. Different personalities make it difficult for Masahito to understand his brother, but he still tries.

Chapters 5-9 are oneshots:
5) Ghost --Setagaya-ku no Maboroshi--
6) Amai Natsu no Kyousoukyoku
7) Unbalanced・Tart
8) Kimi wa Nemuru
9) DEAR / Ganbare! Kagaku-bu

Moriyama Kouta was once an unsuccessful adult manga artist. Due to lack of popularity, he was even on the verge of going out of business.
But one day he became a very popular author with vividly realistic and charming portrayal of his heroines.
The reason for the sudden change in style was that Kouta has taken his younger sister Shizuku as his model......?!

From Yaoi Is Life:

Seina, who's a tattoo artist is entrusted to do a tattoo with a very difficult design by a peculiar customer named Jin. He is confused, but happy his skills are being recognized. Surprisingly, Jin is always meddling in his affairs, and it makes him feel close to him. For Seina, who left home and has a bad relationship with his own brother, Jin is like a big brother he can look up to and put his trust on. But Seina finds out that Jin is actually his brother's friend, and only came to him on his brother's request...

What the young girl rents is not a movie, but a brother, and the wonderful warm feeling of spending time with him. With her parents deceased, and her once kind brother changed... What the girl seeks is the warmth of a family that she once had. Even if it's a rental one.

From Paradise Love Scanlations:

Although they're brothers.Their appearance, personality are completely the contrary!!
Suddenly one day, these two completely different brothers switched souls!? After possessing his cute, girly little brother's body, the hard days of the tough big brother begins.

After being told that his dad passed away, Souichirou comes back to the house which used to be his home 8 years ago. There, he finds out about the existence of his two older brothers - Masato, the eldest, and Kaname, the middle child. In order to receive rights to the house, Souichirou has to live together with them, and despite the chaos and arguments, it's fine by Souichirou if it means he can get the house. But one day, he accidentally sees Masato kissing Kaname...

Si-hyuk finds himself thrust into sudden responsibility when his parents tragically pass away in a car accident, leaving behind his much younger brother, Si-ha, who is two decades his junior. At the funeral, amidst the hushed murmurs of relatives, discussions arise about the uncertain future of the two brothers.

"What's the plan for those two? Who's going to step up?"
"Goodness, now that he's in college, how will he manage to care for his little brother?"
"Wasn't there some insurance payout?"

Amidst the chaos and uncertain discussions, Si-ha utters his first clear words. "Brother. Brother." It's a heartfelt cry, not for Mom or Dad, but for his older brother. Si-hyuk moves slowly toward Si-ha, embracing him tightly. "I'll take care of you," he whispers.

Two brothers, Shunpei and Kyouhei, have very opposite characters but share a crush on their cute sister Anko. The three of them live with their excentric father, may (or may not) have diffferent mothers, have fun, lots of tantrums and try to lead a happy life in junior high school.

From Omanga:

Eiji Otsuka and Sho-u Tajima at it again, Eiji in a much more minor role this time, however. In any case, this a relatively older and short comedy series (4 volumes) that should be a fun break from their usual mayhem with MPD (Multiple Personality/Dissociative Identity Disorder) .

In 1994, this manga was published as a whole under title "BROTHERS High School".

From Neptise Scans:

Dracul's presence threatens humanity and the only ones who can stop them are the Exorcists, siblings bound by blood and granted the power to purge evil. The story centers around Vincent and Ryan and their struggle to become full-fledged exorcists.

Chris Watanabe is a high-school teacher. When his father remarries, he finds himself with an English step-brother named Wataru. Wataru transfers to Chris' school, and just as the four of them are starting their new life together, their parents die in a plane crash. Now Chris and Wataru are living alone together. The elder is cute and the younger cool; what will their new life hold for them!?

From Summer Rain:

Natsume, who works at a game company, learns of his new step-sister the day of his mother's wedding. Just as he starts interacting with the game loving girl, he finds out the feelings the other siblings hold towards this girl…

Brothers Conflict manga focused on Tsubaki and Azusa.

Manga featuring Yusuke's and Futo's stories of how each brother falls in love and tries to get Ema.

Based on events in the light novel series Brothers Conflict and its otome game (visual novel) and anime adaptations.

From AOC Translations!:

The Asahina brothers chase around our heroine, causing a bit Purupuru ruckus! Experience BroCon in a fresh-new style!

The 4-komas retell the events in the light novel in a hilarious twist.

Collection of miscellaneous short stories.

From Yaoi Is Life:

Watanabe Chris is a high school teacher.
When his father remarries, he finds himself with an English stepbrother named Wataru. Shortly after Wataru transfers to the school that Chris works at, their parents die suddenly in an accident. Chris and Wataru begin to live together, and before long they fall in love.
Wataru enters his second year of college still living his happily-ever-after with Chris.

At the same time, Wataru's childhood best friend and former suitor, the cross-dressing Rei, is falling for Yamada, who's always secretly had a crush on Chris...!

In the distant Milky Way, inheriting the best human beings - Sun Wen, Genghis Khan, Einstein, Tesla and other genes, orphans, scattered in the interstellar, to solve the mystery of the destruction of the earth, as Bruce Lee's genetic clone of the juvenile blues Swear to bring all the earth compatriots together...