The sum of stereoisomers formed in the square planer complexes A, B & C in the following reaction sequence. (Ignore Tran’s effects)

${\left[PtC{l}_4\right]}^{2-}\underset{-2Cl}{\overset{+2Py}{\to }}\left[A\right]\underset{-C{l}^{-}}{\overset{+N{H}_3}{\to }}\left[B\right]\underset{-Py}{\overset{+B{r}^{-}}{\to }}\left[C\right], Py- Pyridine$