Packs of dogs or wolves will groom each other during "down time." I would venture to say that is what is going on with your Basenjis. It is a bonding type thing, bonding the pack together. When I saw a pack of wolves in Denali, one of the young wolves had wandered off. The rest of the pack was howling for him/her to come back. When he/she finally did, the alpha came up and sort of rolled him/her, then the rest of the pack all ran over and began to lick his/her face, while he/she kind of cowered down.
It was one of the most amazing things I've ever seen.