Relatives in the Lakota camp? Only real connections I know of are covered in the books I’ve read.
Toppa my head, Isaha Dorman, Custer’s black interpretator/guide was married to a Lakota woman, the Sioux knew him pretty well.
Bloody Knife was raised as a Sioux, he moved with his mother back to the Ree Camp near Fort Buford on the Missouri in North Dakota. He and Gall, probably some others had a sorta blood feud between them.
If there were others, they’ve slipped my mind.
Shrapnel, in LBH and Custer probably knows way more than me.
As far as Montana goes, I rely on him much like I do you and Kaywoodie for Texas!😀
The Crow were mortal enemies of the Sioux. You remember a few decades back, the Sioux had forced them out of the Black Hills and LBH territory. It was rightfully theirs, which is why they sided with the Army.
Reon

"Preserving the Constitution, fighting off the nibblers and chippers, even nibblers and chippers with good intentions, was once regarded by conservatives as the first duty of the citizen. It still is." � Wesley Pruden