Benjamin and Biskit since they both claim to never speak to each other because they're so close to the point where they know what they're saying without saying anything...
And I'm glad they're close because they're both my favourite villagers
I used to have Skye and Fang and they spent a lot of time together, they would ask me many times to send items to each other or ask me to get the other to come to their house. Eventually I ended up shipping them. I miss them a lot though, I have since restarted my town.