When you make an entry and a crew mate is attached to the entry, they will automatically get that entry into their logbook as well and both entries will be authenticated.
So it is best to decide with your crew mates, who will make the entry. lse you will be making double entries.
Also your crew mates vessels will show up on your logbook. So it is best for the owner of the boat to make the entry so that you are not duplicating the boats. That is not really a big deal but it is just cleaner to do it that way.