Well the good news is that it looks like the modified endorsement policy is actually working. The bad news is that it's not possible to use an endorsement policy with an AND condition in BYFN without creating your own client using one of the SDKs.
The issue is that the BYFN script uses the peer CLI to run invoke (and query too) and the peer CLI does not have the ability to collect multiple endorsements. So when you change the endorsement policy to AND, the script is only collecting a single endorsement and therefore validation fails when trying to process the invoke.