It's quite easy to set up, just launch a game with the coordinate sampling tool on (which is in the editor), use that tool by going into your menu in game to find positions of where you want them to go, write all the positions you want for them to hang at down in a notepad, then return to their NPC edit menu and set a possible routine in the NPC editing tool; give NPC A a target position somewhere in town like chairs in the tavern or some place in town, make them face eachother, say that that the activity of NPC A is 'Is hanging around with NPC B', and NPC B 'Is hanging around with NPC A' with their Visible activity being 'Sitting at the table with their friend' or 'loitering with their friend', after you've done that, check either 'random walk' or 'patrol' in the options under that and the AI will do the rest. Honestly you don't need the AI to set that up, you could simply add it to their Lua script as such;
function GetTargetRoutineID(hour)
if hour == (insert hour you want it to happen here) then
return "Is hanging with NPC B"
elseif hour >= (insert hour here) or hour <= (insert hour it happens +1) then
return "silverpine_leisure"
end
You can even make exceptions if you want it to be more immersive, like them not hanging out during a snowstorm by adding something like
else
if World.GetCurrentWeather() ~= "Snowstorm"
return "Hang at home" (or any activity you would create that'd be named like this for when you want them to hang at coordinates at home for example).
You can fine tune it with a bunch of functions that look up the day, weather, season etc, you can see those in the lua script tab of the NPC editor when you press 'copy documentation' which gives you all of them in your clipboard.
If you mean you'd like them to organically meet with eachother without instructions at random times, then you could just put a routine like 'Hangs around with NPC A/B' as a description, give them both a general meet up point at certain coordinates, then check the dynamic routine writer on and hope the AI generates something for them at random.
Either way what this will do is have them just be near enough eachother to trigger a group conversation, and the activity and NPC lookup will probably make the AI improvise them talking with eachother and acknowledge that they were in the middle of a discussion or activity when you talk to one or both of them at their meeting spot.
If however you meant to say that you'd like the two NPCs to hold conversations, share information and such, I'm sorry to say but none of Silverpine's NPC can do that, the only real 'conversation' or rather NPC to NPC interaction possible that isn't directly controlled by the player is if during one of your conversations one NPC commit to loose memory a 'I will talk to X about that thing that I want to talk to them about after the player initiated conversation with me', and it's usually just a one sentence phrase they'll eventually repeat to another NPC without much context whenever they see them (If possible they usually just decide to rush the other NPC and tell them that sentence immediately).
Well, that or you threatening them or loitering in their house without their authorization, which has them calling for the guard, which breaks the conversation and has them run for Aldric who will then chase you around town to get an explanation from you.
And also that other exception with that one NPC that always ends in your demise... but anyways I digress.
Point is they never actually hold actual elaborate conversations that generate memories for them passively, it's always reliant on you as the player conversing with them.