How do you guys handle a monster’s initiative when it’s far away from the main combat?

Imagine my players are coming up on a Goblin fort, and notice some are cooking a baby or something. They want to get sneaky and attack the baby cook and his sous-chef, but they don’t want to alert the entire camp if possible.

How do I handle this? Does it depend on how much noise has been made? Stealth checks? Distance between these goblins and the rest of the goblins? All of the above? Does it matter whether they kill the two baby cooks in one turn/one action, or does it depend on other factors?

Thanks in advance. I love this community.