Severus barely had time to react to Thaor's spell, thanks to Jack, he was pushed out of the way, the spell jetting past his face, missing by inches. The others all seemed like they didn't want to harm Thaor, however, Kye had no personal ties to the man, other than he is the former Deputy Minister. Kye wouldn't just sit there as Thaor kept attacking the Minister, the Chief Warlock, and several aurors.
If you aren't willing to take him down, then leave child. Sev snarled at Jack, he really should have shown more appreciation for her saving his life, but it was a dangerous situation they were in, Thaor was showing no regard for human life, therefore, deadly force was warranted.
I believe the time for only defensive spells has passed, he obviously has shown no regard for the lives or safety of others, and last time I checked, attacking the Minister of Magic warranted a dementors kiss, and deadly force if necessary. Sev said has he stood back up.
Sev turned his wand on Thaor, Stupefy! He said, sending a jinx at the mans chest.