I think much of the problems people have had with trigonatus in groups in captivity have been due to small and poorly-designed enclosures. They have a reputation as being more aggressive than palpebrosus, and I believe this to be true. However, this should not be a factor if you have a good enclosure, and are comfortable with the handling and maintenance of the crocs. If you want any info on that, I'm happy to tell you more about it. Crocs are not silly, and the aggression is usually either a defensive mechanism, or a very strong feeding response.
Curiosity also plays a part.
They will be much more relaxed this way. This is where the caimans spend much of their time.