One thing to keep in mind is that in 5e players don't 'use skills'. They describe what their character is doing. Then the DM decides whether they succeed, fail, or if the outcome is uncertain. In the latter they usually make an ability check which may add proficiency if the DM decides a certain skill applies.
Here is how we play:
- The DM introduces the scene.
- The DM then asks each player what their character is doing.
- The DM then resolves the events in an order that makes sense.
Example:
The characters enter a room in a dungeon which appears to be an old musty library. A person who looks completely out of sorts is sitting at a table. The players have a brief conversation with the person in order to establish the scene. Things like who are you, how did you get here, what are you doing, etc.
Then the DM says, okay what are you doing?
Player 1 - I search the library, I want to see if anything has been recently moved or taken, pay attention to things like if something looks like a different age than the rest, that sort of thing. I don't want to disturb things too much just yet so I don't tear things apart.
Player 2 - I help in character 1's search. I have the Guidance spell so I'm going to cast that for them too.
Player 3 - I want to get to know that NPC more. Find out what they know about x, y, and z. I don't trust them so I'm going to ask them about the same things different ways, see if anything is up.
Player 4 - I stand guard by the door that we haven't been through yet, keeping my ear to it but also looking out into the room for anything that might jump out at us.
Resolution:
Player 1 and 2 it is pretty easy to spot that there appears to be a missing scroll tube as there is a spot without dust. The other scroll tubes in the area appear to be historical documents like maps. The rest of the books appear to be mundane affairs of ancient history, texts on stonework and smithing, that sort of thing.
Player 3 - The NPC tells you what they know about the questions you asked. Give me a Wisdom (Insight) roll to determine if you can tell what sort of state they are in. Okay, so at first you thought their strange manner was just a result of lack of food and rest, but after a bit you have noticed that every time you asked for anything of importance they paused for a bit and their face went blank of emotion. Something is not quite right here.
Player 3 - 'Okay I tell the others, I don't have a good feeling about this'
Player 4 - Make a Wisdom (Perception) check. Okay, you hear strange noises from beyond the door. They are a deep sound, and rhythmic, almost like breathing. Only more like a large body moving about but you hear no footsteps.
Okay, quickly, everyone what do you do? The characters have a few seconds to assess the situation - something terrible is coming - Do they guard the door? What do they do about the NPC? etc.
In a purely social encounter I ask the players what they are going to say - One player will either say it or describe what they are saying. Based on the NPC they might again succeed, fail, roll perhaps with advantage or disadvantage. Then another player gets a chance to say something if they want to, and so on until everyone has engaged with the NPC. There is no 'help' here, you're either talking to them or not. Though, maybe if you had an ability like telepathy you could help them, coaching on what to say. These sorts of things are what the DM is for.
If a fight has broken out the PCs can still talk to the people they are fighting, in that case they get to say something on each of their turns.