They should be able to use improved knockdown even in vanilla nwn. But the usage of these feats is coded very poorly and works a bit clunky, especially on a high levels like 40.
As for Taunt, there are several choices.
1. Create your own AI for specific creature. I assume you dont want to go this advanced route so I wont provide details its a bit complicated.
2. Use my community patch, but you need 1.72 beta8 its not present in version 1.71, you can find it here
3. Install custom AI set like Jasperr AI and assign this AI scripts to your creature. Jasperrs AI definitely has this feature, cant speak of other AIs though.