separating names

Hello,
Hoping for some assistance please. I have along column of names and am trying to have them separated as per example in Col B sheet. When there is a double set of names with different last names then I only wish to have the first name in ColB formatted as per sheet. If there is a combination which has the same last name with different first names then I would like to have only the last name and first first name. The last name in the sheet is the more common format of first and last name.