Róisín, I think I've been assuming that as well, though I didn't have it as clearly thought out.
It does make sense to me; though I don't think we've enough information to know for sure.
In any case, even if they're only going to die if Emil goes in there, that seems enough to me to allow for drastic measures to save their lives. And I don't see any reason to think that singing would work better than shouting, which Lalli already tried unsuccessfully. That is, maybe there is some such reason; but we haven't had any evidence for it, so maybe there isn't -- and Lalli would know better than we would. If singing at people entranced by trolls usually breaks them out of it, I would think this would by the year 90 be well known both to scouts and to mages.
It's true that Lalli chants when he casts at least some spells. But it's also pretty clear that doing such chants requires both time and concentration/psychic energy. He hasn't got the time, and it's very likely that he hasn't got the psychic strength right now, having used it up saving Emil's life earlier -- in a situation in which he seriously endangered himself by doing so, although simply leaving Emil to die and continuing to run away would almost certainly have kept him safe.
