By using system above, I found Y(z) as below, using this, can you answer part d, e, f correctly?
\begin{equation}
Y(z) = \frac{1}{2}(X(z)H_0(z)G_0(z)) + \frac{1}{2}(X(-z)H_0(-z)G_0(z)) + \frac{1}{2}(X(z)H_1(z)G_1(z)) + \frac{1}{2}(X(-z)H_1(-z)G_1(z))
\end{equation}
d) Show that the overall system is not necessarily LTI for arbitrary filters $H_0(z)$, $H_1(z)$, $G_0(z)$, and $G_1(z)$.
e) Show that the overall system is LTI if $H_0(-z)G_0(z) + H_1(-z)G_1(z) = 0$.
f) Show that if $F_0(z) = H_1(-z)$ and $F_1(z) = -H_0(-z)$, the overall system is LTI