Hi there. Keeping the dog separate and upstairs from your bunnies is a good idea. Small dogs aren’t always even tempered, that’s more to do with upbringing than anything else but I understand what you mean as opposed to something boisterous like a staffy or pitty type which have boundless zest for life and can be rough by accident.
Your buns may or may not be upset. It’s tough to predict how they may react. They will certainly be able to hear and smell the dog, the smell may be an issue for them at first but they may get used to it. When I first got Apollo and Luna, if I came home from my friend’s house with the smell of their dog on me, he would thump, run and hide from me because the smell scared him. Now not having interacted with a dog or having any other experience with that smell than on me, they don’t care anymore. So just be prepared that buns may be scared, or even aggressive towards you if you have the smell of dog on your hands or clothes.