Excel - conditional dropdown list based on another cells content

I'm using MS Excel 2010

I'm creating a form which must be signed by signed by two people. I have two lists - Group A signatories, and group B signatories. Group A people can approve payments of £25,000 and over, but group B's can only approve payments up £25,000. Each form needs to be signed off by two different people. I want to create a drop-down list whereby if a user enters an amount of £25,000 or more in a cell (say J10), then the dropdown list will only list the group A signatories. Furthermore, the dropdown list should exclude the name of the group A person who has already signed the form once in another cell (so you can't have the same person from group A signing the form twice).

I've tried this, but it's not quite appropriate for this situation I don't think.

Hopefully this makes sense :)