Trying calculate the value of one cell depending on value of two different cells

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On my sales log, I currently am able to calculate the number of units sold by each sales person even if the deal is a split deal giving each person credit for half of the deal (thanks to the help I have received from this forum). Now I am trying to add a column on the second worksheet of the attached sample log to automatically sum all of the gross each salesperson has generated. If the "sales2" column is blank, the salesperson listed in "sales1" receives credit for all of the gross in the "total" column; however, if there is a salesperson listed in "sales2", them both salespeople only receive 50% of the value in the "total" column. I have tried many different formulas, without success.

Thank you in advance for any help or advice.

SAMPLE LOG.xlsx