After B makes their decision, now A's turn to accept or decline the penalty. But where would the spot of enforcement occur for team A.(Team B's penalty of unsportmanslike celebration)
I'm fairly certain I have this correct. I was waiting from one of the experts to chime in on specifics, but here goes ...
It's less complex than sounds (more often than not, both will choose KO and all is right in the world again).
Answering your Q, the enforcement spot for A on Bs foul will be determined by Bs decision on A foul. Possibilites are: R3 or R1-1/2 for PAT or K40 or R45 on KO.
Get Bs decision first (making sure he knows A has a decision based on his decision; then inform him that's it; no take-backs) then tell A what B decided and tell him his options.
There are 4 possibilities depending on who decides what (B option first).
>B opts KO (PAT spot 3YL; KO spot now R45)
⦁ A opts KO: PAT at 3YL and B KO from K40 (like nothing happened; most likely scenario)
⦁ A opts PAT: PAT from 18YL (but B KO will be from R45)
>B opts PAT (PAT spot now 1-1/2YL; KO spot K40)
⦁ A opts PAT: moves PAT to 16-1/2
⦁ A opts KO: PAT at 1-1/2 and B KO from K25