When In-Laws Become Brothers and Sisters

A brother- or sister-in-law becomes real family the way anyone does: through small, repeated welcomes. A seat at the table that's theirs. Their name said right. A place in the family photo. Time with you, not only through your sibling.

This guide is for both sides: the family making room, and the person marrying in.

Family grows by marriage

When a brother or sister marries, the family changes shape. Researchers at UC Davis note that leaving home, getting married and having children all transform sibling relationships in early adulthood (opens in a new tab) (Conger and Little, 2010). Your sibling now has a partner who comes first in many ways. That can feel like a loss, even when you're happy for them.

It can also be a gain. You can get a new brother or sister, and their family can become part of yours.

In many families, especially South Asian, Middle Eastern, African, Latino and other immigrant families, marriage joins two whole families, not just two people. In others, in-laws stay more distant. Neither is wrong. What matters is that the people involved talk about what they want.

What the research says (and doesn't)

There is surprisingly little research on brothers- and sisters-in-law. A Vanderbilt team studying families of people with disabilities called the sibling-in-law an "unknown member" (opens in a new tab) and noted how little attention they've received. In that survey of 102 siblings-in-law, about half rated their experience positive, about a third mixed and about 15% negative. Those who better understood what to expect before marrying in tended to do better.

The closest general evidence is about mothers-in-law. Researchers at the University of Texas at Austin followed 60 engaged adults and their mothers from before the wedding to after it. When in-laws had their own contact and positive feelings before the wedding, ties were stronger afterward (opens in a new tab) (Fingerman and colleagues, 2012). Negative expectations before the wedding predicted a more negative relationship later.

It's a hint, not proof, for siblings-in-law. But the hint is clear: the in-law bond that lasts is the one you build directly, not the one you inherit through someone else.

Making room for a new brother or sister

If your sibling is marrying, here is how to make room:

• Learn their name and how to say it. Use it often.
• Go one-on-one. Coffee, a drive, a phone call where your sibling isn't the go-between.
• Learn about their family. Their parents' names, their own siblings, where they grew up.
• Save them a seat. At meals, in the family photo, in the group chat.
• Include them in traditions and explain them. Don't assume they know the rules of your family's Eid, Diwali, Christmas or birthday rituals.
• Invite them to something without your sibling. It tells them they're wanted for themselves.
• Ask the quieter questions. What do they miss about their own family's holidays? What food reminds them of home?

If you're the one marrying in:

• Learn the names, and the nicknames.
• Learn the jokes and the stories, and ask for the ones you don't get.
• Turn up to the dinners you could skip.
• Ask the youngest sibling what they're into, and listen to the answer.
• Share your own family's traditions too. Making room goes both ways.

Small check-ins matter more than you'd think. In experiments, people underestimated how much others appreciate being reached out to (opens in a new tab), and the gap was larger between people who weren't yet close (Liu and colleagues, 2023). A text to a new sister-in-law on her birthday is likely to mean more than you expect.

Different families, different traditions

Two families often do things very differently: how loud dinners are, how money is handled, who hosts holidays, which language is spoken at home, what role elders play, how religion shows up in daily life.

• Be curious, not judgmental. "How did your family celebrate this?" opens doors.
• Translate for them. If your family switches into Bengali, Spanish, Tagalog or any other language, catch them up, or teach them a few words.
• Explain the customs. Wedding rituals, food rules, what to bring when visiting elders. Don't make them guess.
• Don't stereotype either family. People are more than where they come from.
• Blended families have their own layers: step-siblings, half-siblings and ex-partners. Go slowly, and let relationships form at their own pace.

When it's awkward or tense

Not every in-law relationship is easy.

• Stay polite and present. You don't have to be best friends to be family.
• Don't vent about them to your sibling. It puts your sibling in an impossible spot.
• Speak to your own sibling, privately, if something needs to be said. Not around them, and not through your parents.
• Assume good intent first. Ask what they meant before deciding they meant harm.
• Never ask your sibling to choose. That damages your relationship with your sibling, not just with the in-law.

Sibling researcher Megan Gilligan told NPR that with family tensions, it's not a good strategy to let it go (opens in a new tab). Address it kindly and early. If the relationship has already broken down, see how to repair a relationship with a sibling.

In-laws as part of the family's story

Over time, a sibling-in-law becomes part of the family's memories: the photos, the inside jokes, the holiday stories. Tell those stories with them in it. Teach your children to call them aunt or uncle, or whatever your family says. When you tell your siblings what they mean to you, include the ones who married in.

The Amin Foundation knows this personally. In August 2022 the Amin family lost Basir Amin, 18, and his brother-in-law Afrid Haider, 34. Afrid is remembered as a brother. Chapter 23 of Enduring Bonds, the memoir by our founder Faruque Amin, is about how someone who marries into a family becomes a brother. See the Enduring Bonds companion for every page linked from the book.

For more on everyday closeness, see showing up for your siblings. If you're raising children, the welcome starts at home: see how to raise siblings who stay close.

What you can do today

• Send your sibling's partner a message that isn't about your sibling.
• Learn the names of their parents and siblings, and use them next time.
• Invite them to one thing on their own: a coffee, a game, a walk.
• Explain one family tradition before the next holiday, so they aren't guessing.
• Add them to the family photo and the group chat, if they aren't already.