Isaea is a slaver, and the slavers deal with trolls. It’s certainly possible that the trolls at the Keep are acting coincidentally, if not independently, but there’s no doubt that the “Stronger” that Torgal refers to is a Roenall (or a representative of). Despite most of the trolls in BG being erroneously given an Intelligence of 16 in their CRE file, trolls are supposed to have Low intelligence (5-7). That’s borderline retarded, and certainly illiterate. Combined with their fearlessness and Chaotic Evil nature, any kind of coordinated attack, like the one seen at the Keep, would need multiple handlers capable of keeping them all in line. Torgal is given only an 11 INT, and the fact that he is somehow immune to being tricked, bribed, or otherwise swayed from betraying his benefactor, is a massive failure of design. Chaotic Evil doesn’t feel enduring loyalty as Torgal displays. In fact, betrayal in this situation is pretty much a defining feature of that alignment. Another is the respect or fear given to those more powerful. Despite Isaea having control of a portion of Athkatla’s military, Charname and his smaller force have, at that point, displayed at least as much power, and a much more immediate threat. Torgal should be taking the money and running.
Would Nalia’s aunt, Lady Delcia, have worked with Isaea to bring about their mutual goal of the Roenalls in charge of the Keep? Possibly, and even if not, she certainly benefits from the results, if not the methods. In any case, she had no real ability to influence events at the Keep, other than a promise of reward if things went her way.
Glacius seems to be the lynchpin. I cannot handwave away the fact that he was somehow “permanently” charmed, yet still retain enough functionality to command the trolls in accord with Roenall’s wishes. There is no spell capable of this, outside of a perfectly phrased Wish. Regardless, the only explanation is that Roenall must have hired a mage to ensorcell Glacius, the obvious partner being a Cowled Wizard.
These revelations of basic logic can help rectify an otherwise ludicrous plot, and provide the player with more options for how to resolve it, besides the too-often-available “kill everything, sort it out after” option.