this will work, but it's not clear for me what you want, because on the first name, you remove third name and you switch places between the two names left... And , on the next row, it is a different situation. You want a different formula for every row??
Try: (works on second row, for the first row you have to be more explicit)
=LOWER(LEFT(B4;FIND(",";B4;1)-1))&"."&LOWER(RIGHT(B4;LEN(B4)-FIND(",";B4;1)-1))