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This sequent is provable.
\begin{logicproof}{2}
(p \imp (q \imp r)) \land (q \imp (r \imp s)) & \prem \\
\begin{subproof}
p & \assum \\
p \imp (q \imp r) & $\ande{1} 1$ \\
q \imp (r \imp s) & $\ande{2} 1$ \\
q \imp r & $\impe 2,3$ \\
\begin{subproof}
q & \assum \\
r & $\impe 5,6$\\
r \imp s & $\impe 4,6$\\
s & $\impe 7,8$
\end{subproof}
q \imp s & $\impi 6-9$
\end{subproof}
p \imp (q \imp s) & $\impi 2-10$
\end{logicproof}