I break Triggers down by a 1-5 Aggression Scale
1-Xanthichthys family...Sargassum, Bluejaw, Crosshatch, Goldback...These are a pretty safe bet by Trigger Standards.
2-Black Hawaiian, Indian, Pinktail, and the not so common Sufflamen family (Lei, Halfmoon, etc.)...A little more risky, but not too bad
3-Niger, Huma, Rectangle Huma, Assasi, Starry....Starting to get more risky
4-Clown, Bursa, I haven't been brave enough to try one yet
5-Undulate, Queen, Blueline, Titan, Goldenheart (Goldenheart is pretty new to the hobby, and a lot of people finding less aggressive than Queen)....Do not play well with others.
All triggers belong with fish capable of defending themselves in my opinion, my Sargassum is a great fish, but he is not exactly a Goby either, he is the only fish in my tank to stand up to my Sohal ever.
On to your specific question....
IMO, your Niger and Pinktail can handle themselves with a Clown just fine, what other fish do you have though? Most other fish would be in danger with a Clown as he ages, about the only fish I have seen stand up to a Clown Trigger are big Acanthurus Tangs (like Sohal) and a Passer Angel.