You can sit on a bench behind the Ronan's House or in the Locker Room of the Police Station to talk to your other twin! You do not need to exhaust the dialogue, you can leave the conversation as soon as you are able to and still get the achievement!
Here is a video guide with all the missable achievements! One of the ways to get the We Need To Talk Achievement starts at 7:36!
The timestamps for all the achievements and collectibles are in the description! Hope this helps!