Not sure if I should use Match or Vlookup, or how in this situation

On sheet1, ColumnA I have a list of employee names from row4-row200. In row 1 from C:AG, I have a list of dates. For each name, I have a number of hours worked for that employee in the corresponding cell according to date.

Now what I'd like to do is be able to sum these totals according to calendar week (week starts on Sunday, ends on Sunday) on sheet 2.

So on sheet2, I have the same set up with names, but instead of 31 dates in row 1, i have just 5 from C1:G1. Entereing in a date in C1 changes the dates in D1:G1 accordingly. So, how do I get a weekly total depending on the dates in row 1 of sheet2?