You can remove #include <engine> as engine is not needed.
client_death is a csx forward so you need to include it.
You must use pcvars and learn how to use it.
PHP Code:
//Check if Award Grenades is enabled
if(award_nades == 0) return PLUGIN_HANDLED
Correct way :
PHP Code:
//Check if Award Grenades is enabled
if(get_pcvarnum(award_nades) == 0) return PLUGIN_HANDLED
There's a lot of other errors.