Even sisters who love each other get into the occasional fight, and when that happens Granny Smith has to put her hoof down.

Twilight Sparkle visits her brother in Canterlot and witnesses more than she expected to. Contains non-sexual disciplinary whipping/spanking.

Cadance gets to watch young Twilight Sparkle overnight for the first time. Things do not go well.

Pinkie finally pushes her employers' patience too far. Contains non-sexual disciplinary spanking.