Hello! I believe one of the stories you are looking for might be
Pack by
NicoRavenPen
The scene you are describing happens in two chapters,
Chapter 27: Of Cramps and Comfort and
Chapter 29: Jealousy and Surprises
Although, I don't think Sesshoumaru or his inner inu ever thought about impregnating a female inu just to get a full-blooded inu heir in this story...
Unfortunately, I don't know the other two stories, but I hope you find them!
Happy Readings~!
EDIT BY WICCAN - This story is rated M, NO YIMs!!