Being invisible does not hide your location on the map, using the hide action does. You do not get advantage to stealth checks because your are invisible, you cause sight based perception checks to auto-fail. 4 creatures inside a darkness spell know each other's exact locations, there is no guessing, you still roll with disadvantage on attacks because you cant see them, but you can always hear them. I see this easy and simple rule bastardized so hard in games that I have to start asking my DM if they are going to hombrew the stealth rule before a campaign starts.
There are two things at play. First, the rules are quite vague in several areas. Second, when we have vague rules it's up to the DM to interpret the rules in such a way that make sense.
For invisibility and darkness, the rules are actually quite sparse. Someone in darkness is effectively blinded.
Blinded
• A blinded creature can’t see and automatically fails any ability check that requires sight.
• Attack rolls against the creature have advantage, and the creature’s attack rolls have disadvantage.
Under invisible it says
Invisible
• An invisible creature is impossible to see without the aid of magic or a special sense. For the purpose of hiding, the creature is heavily obscured. The creature’s location can be detected by any noise it makes or any tracks it leaves.
• Attack rolls against the creature have disadvantage, and the creature’s attack rolls have advantage.
That's pretty much all I can find as written on page 105 of the basic rules.
Note that the location "can be" detected. Not "is always" detected. In addition "noise it makes or any tracks it leaves." What happens if it's not making noise or leaving tracks? A flying creature in a zone of silence in the dark is going to be undetectable in most cases.
So when you state that "creatures inside a darkness spell know each other's exact locations", I disagree. The rules don't state that anywhere. If you walk into an area of darkness with an iron golem and it hasn't been activated yet, I would rule that you have no way of knowing it's there (barring other magic). It doesn't breath, it isn't moving, it is literally making no sound.
The only way to detect the golem is to stumble into it since the only way to perceive it would be to see it, which you cannot do.
If the golem activates because you enter the area and it starts moving, you can hear it and now you may know something is out there. You may even have a pretty good idea of it's location depending on the situation, but it's not automatic. The way I run it, you may not know exactly where it is until it attacks. At that point you can target it with disadvantage (because you are effectively blind).
I agree that this does leave a lot up to the DM and different DMs are going to rule it differently. That may bother rules lawyers (not saying you are one or that it's even a bad thing) but it's just part of the structure of 5E.
So yes, you have to ask your DM how they handle stealth and invisibility. I think the DM making rulings based on common sense when the rules aren't explicit is a strength of 5E, not a weakness. Feel free to disagree.
Oh, and if I'm missing a rule somewhere feel free to point it out. Wouldn't be the first time. 