You may want to change your data model before you get too far along with your current structure.
Whenever you are adding "2" to a field name it's a pretty good indication that you should make a new table. So instead of having "salesperson" and "salesperson2" two fields, you would add a new "ORDERSALES" table with the following fields:
ID - primary key for the table
orderID - foreign key, the primary key for the ORDERS table
salespersonID - foreign key, the primary key for the SALESPERSON table that contains all of the sales employees
commission - number, the amount of commission earned for the sale
Putting the commission field in this table enables you to record situations where they don't allocate the commission 50-50. Then you can put your summary fields in this new table as well for your sub-summary reports.
If it makes a difference my commissions are in a different table.
This has all the sales order information including the saleperson
This contains all the item information including model info - sell prices - commissions
Right now I have salesperson field in "Items" set as a look up back to the "Orders". I was hoping that there was a way that I could create a field in the items table that looks back at both salesperson fields in "Orders".
Can we assume the ORDER totals the Commission from all of the ITEMS sold as part of the ORDER?
The idea of the table to join a SALESPERSON to the ORDER is that you can set the Commission allocation on a per-salesperson basis. So by default you might auto-enter 100% of the ORDER Commission for the SALESPERSON but if there is a second (or third) SALESPERSON you can further adjust their commission.
This structure satisfies your desire to search for a particular Salesperson and see all of the Orders in which that person played a role. It also satisfies your desire to create a report that can total all of the Commissions for the Salesperson. And it's flexible, allowing you to have multiple people involved in the order each receiving commissions and not necessarily in an even split.