Twins

"...and a Million Years Gone By" by Dscully141
...And So It Begins by Montana1416
Angie series by X Firelady
Baby Plans by Kristen
Babysitting by Binky (Scully's cousins)
Babysitting II. Somersaults by Binky (Scully's cousins)
Babysitting V. Baby Shower by Binky (Scully's cousins)
Babysitting by Tabby
Being Young series by Jo Ann Medrano (prexf Maggie Scully - Bill jr. and Missy are twins)
Calm Before the Storm by Eileen Whipple
A Challenging Life by Billie Reid (Kim/Skinner)
Christmas in (Haven) Maine by Neoxphile and Faerax
Christmas Time is Here Again by hellogoodbye57
Chosen One by Peach (m/m)
The Climb by Starbuck2824
Could've Been by Rogueangel
Daddy's Girl by Starrlyte
Deliverance From Evil by Jacquie Lava and Tess
The Discovery Series by Erin Blair
Ersatz Matriarch by Jeri
Family I - The Beginning by Kelly Mullins
Family II - Trials by Kelly Mullins
Family III - Changes by Kelly Mullins
The Family G-Man by Neoxphile and Felinefemme
The Family G-Man: One Fine summer by Felinefemme and Neoxphile
The Family G-Man: Confessions and Connections by Neoxphile and Felinefemme
The Family G-Man: IWTB by Neoxphile and Felinefemme
The Family G-Man: From Here to Paternity by Neoxphile and Felinefemme
A Favor for Scully by Scarlet Scully
Final Truths by Lexy Torell and Psi Fi (Krycek/Samantha)
Fiducia e Verita by Bluerose
Five Years by xfilesjunkie
Flight into Egypt by Vickie Moseley
Folded Like a Saint by kim1013
For the Good of the Child by Aislinn Carter
The Generations series by Macspooky & Co.
Great Expectations by bellefleur and Emily Sims
Great Men Universe: The Beginning by The Phile Formerly Known as Soapie
Happy Birthday, Baby Boy by Squishy
Hermaphrodite by Jo B(slash)
I Know What You Did... by Henle Girl
I Shall Believe by Cathey Scully
I Turn to You by Devin (prexf Maggie Scully - Bill jr. and Missy are twins)
If Alex Fell series by Frohike
In the Here and Now by shadowfoxsmate
Inherently Given by Michelle Hiley and Vickie Moseley
Innocents by Peach (slash)
Iolokus V: Syadiloh by Mustangsally and Rivka T
The Island by mercury_999 (nephews)
It Just Happened by Mystic
It's Only Ever Been You by kimo-sabe
Joy Begets Sorrow by Parrotfish
Joyful are the Waterdrops by kim1013
Labor Day by Billie R
The Last Deception by Susannah
Life From the Ashes by Jo B (slash)
The Life They Now Lead by Lilxgirl (aka Abigail)
The Lone Gunmen Babysit by Chris M.
The Lone Gunmen Babysit II. Dinner by Chris M.
The Lone Gunmen Babysit III. TV Junkies by Chris M.
The Long Trail Home by Nantglyn
The Lullaby series by Donnilee
Miracle Season by Neoxphile
Mirror of Love by Tanja
My Family by Spookster
Nightmare series by aka "Jake"
Nothing's Ever Normal by hellogoodbye57
Origins by Mischa
Our Sweetest Songs by Jamie Taylor
Places That Scare You by Rose Campion (slash)
Playing House by mercury_999 (nephews)
Possibilities by Jennifer Sweeney
Perceptions by Laura (slash)
Pregnant Mulder by Bertie (slash)
The Present Implies Presence by kim1013
Reason For Hope by crisrbn
Recovering Gemini by Neoxphile
Requiescat by mackillian
Return to Me by Ladyraider
Rising Again by Rocketman
Running Lessons by Maybeamanda and Spookey247
Sarah Companion: Stephanie - Twins by Patty Hayes
Secrets of the Gemini by Jei
Showers, Dreams and Baby Elephants by Joey R.
A Sleepy Little Town: Memory House by Neoxphile
A Sleepy Little Town series: Free Fall by Neoxphile
Sweet Dreams Series by Alice J. Foster
This Fragile Universe by Neoxphile wip
The Time For Miracles by Carol Gritton
Truckin' II: Keep On Truckin' by Donnilee and Fatcat
The Truth is Not Enough Part 2: Children by dana-maru1
The Truth Is Not Enough Part 3: William by dana-maru1
The Truth is Out There by Lolabeegood
Twins by Teetee
A Twist Of... Series by Erin Blair
An Unexpected Delivery by Colleen
Wassail: an X-Files Christmas story by Julie L. Jekel
We Believe by Anonymous and Lizzi
Whatever We Become (Seed II) by Cathey Scully
When Love Gets Lonely by Pinkholyone and Louise (Doggett/Reyes offspring)
Where the Heart Lies by hellogoodbye57
Without You by Jennis524
Womb For Revenge by Neoxphile (Mpreg but het)
Wonder Years by Billie Reid and Kyouryoku Senshi
The X-Files Chronicles by Madame F

Triplets

And Baby Makes Four by gillian dana
And Baby Makes Four Returns For Halloween! by gillian dana
Baby Mine by Debbie Gramlich
Beyond The Truth by Neoxphile (Doggett/Reyes offspring)
Day Becomes Night Day Becomes Night by Jamie Tanquary (other characters' offspring)
Deconstruction by Entil'zha
Five Years by xfilesjunkie
Happy Birthday Mulder Triplets! by gillian dana
I Should Have Known by Ellethom
Life From the Ashes by Jo B (slash)
Meant To Be II: Children by Jinxd n cursed
Retam Sullet by Onemillionandnine
When Love Gets Lonely by Pinkholyone and Louise (Doggett/Reyes offspring)
Who Knew? by Ellethom

Quads

Quints or more