Budgernaut: you know that you cannot "choose" to engage 3 trolls in a single round. When engaging enemies, you can engage 1 of them optionaly. Then, all enemies with an engagement value higher or equal to your threat engage you automatically.
Since all the unique Trolls have a 34 engagement value, if your threat was 34 or more when they showed up, they would all engage you at once. If it was less then 34, you could only engage 1 of them optionaly, not 3.
Maybe I misinterpreted your post; sorry if that's the case.