im not familiar with the -5 penalty on darkvision...can you show me what book this is referenced in?
Players Handbook.
Section on Light and Vision states: "Within a specified range, a creature with darkvision can see in dim light as if it were bright light and in darkness as if it were dim light[.]"
So if your dungeon is pitch black, it is dim light for those with darkvision.
Higher up in the light and vision section, it says the following about "dim light": "Dim light, also called shadows, creates
a lightly obscured area."
In the same section, above this, it says the following about lightly obscured areas: "In a lightly obscured area, such as dim light, patchy fog, or moderate foliage,
creatures have disadvantage on Wisdom (Perception) checks that rely on sight." [emphasis mine]
In the section on "Passive Checks" in Chapter 7("Using Ability Scores") it states: "If the character has advantage on the check, add 5. For disadvantage, subtract 5. The game refers to a passive check total as a score."
So that is how you get -5 on passive checks when using darkvision in an area with no light.
As for my games, when using my VTT, light, vision, and line of sight rules are strictly enforced. In VTT with manual reveal (e.g. didn't have time to prep the VTT map by tracing walls, etc.) I reveal/describe based on the character with the best vision. In TOTM I generally get a bit fuzzy in how I handle it but I try to describe based on character sight.