Create Radio Button List from Selection

I am trying to build a radio button list of amounts selected from a field.

Fields on Form:

  • Company Name
  • Open Invoices (checkbox generated when the Company Name changes)

I would like the Radio Button List to contain:

  • Total Amount - Amount calculated via sum(InvoiceAmt) from all the open invoices for the company selected (this is working)
  • Selected Amount - Amount calculated via sum of the elements selected in the Open Invoices Field (not working)
  • Custom Amount - If this option is selected, the user can enter the amount they wish to pay in a field that is enabled upon selection (not working).

Questions:
How do I create a radio button list for these values?
I am also unable to get the OnChange ajax event to execute when open invoices are selected.