Social distancing rules
Elbow bumps only
why does the on the cheek need to be added?
Because faire la bise means to greet or say farewell with (a) kiss(es) on the cheek(s).
As the sentence is referring to Léo & his brother (3rd person plural), the present indicative conjugation of faire here is font.
Because they stress the kiss is fraternal rather than erotic. La bise is absolutely platonic, but "kiss" can have different meanings in English.