so the format is always the same, 1st name, followed by a space, then last name, followed by a ,?

in other words, if we can extract just the last name, we can sort on that? if so, in a new column, assuming your data starts in A1, try this formula to extract the last names for sorting....

=MID(A1,(FIND(" ",A1,1)+1),(FIND(",",A1,1))-(FIND(" ",A1,1)+1))