§1. When several persons have been delegated in solidum to transact the same affair, the one who first begins to deal with it excludes the others from doing so unless that person subsequently was impeded or did not wish to proceed further in carrying it out.
§2. When several persons have been delegated collegially to transact an affair, all must proceed according to the norm of can. 119 unless the mandate has provided otherwise.
§3. Executive power delegated to several persons is presumed to be delegated to them in solidum.
Source: Code of Canon Law (Vatican.va)