Unable to populate BP_REL fields in UI

Hello Experts,

I am unable to add BP_REL fields in UI.

below are the steps which I have followed.

1. Created UI from Scatch using "USMD_ENTITY_UALUE2"

2. Added main entity "BP_HEADER" and "BP_REL" and added UIBB Component shown in below screen under "BP_Header"

3. When try to create UIBB Compnent under BP_REL I am unable to see any BP_REL related fields such as "Partner 1", "Partner 2" , Category, or anything.  Not sure what I am doing wrong.

Also, part from this issue I would like to know that how I can add buttons under "Tax Information" section which allows users to add, remove or update Tax number category information?

Thanks,

Meghna