I talked to our USCIS just now. The woman I spoke to is going to check with the officer in charge because:
My home study approves us for one female infant, or twins.
The agency's approval states we are approved for up to 2 infants.
It may be fine as is. If not, then we may submit an addendum from our home study provider (approved by the agency) stating that since twins are not available, we would like to adopt 2 unrelated infants, and have been approved to do so.
Pretty simple!
Thanks for all your input.
Jenny