https://66.media.tumblr.com/0edfda268c82a58e2bbdf00153c5fc4e/tumblr_ml02uguik41r5yd9po1_1280.jpg
Inspired by tandems, if the distance between the front and back seats is sufficient, it can keep the two people in 1.5 meters
As I am not sure whether the bicycle chains and gears can support such a distance, we could also combine two monocycles with a beam
Face to face is better than face to back as for fostering social encounters, and in this way they can move both forward and backward while maintaining 1.5 meters distance.
If we change the beam into a circle, then it can contains more people and it is much easier to keep balance.