Option 1:

  1. Create a gift on one constituents record
  2. Add a soft credit to this gift for the other constituent.
Option 2:
  1. Create two separate pledges, each for half the amount of the requested pledge.
  2. Record the pledges on the appropriate constituent records.
  3. Soft credit the other constituent on the pledges.
  4. This route will allow you to send 2 separate pledge reminders.