At the moment only the one character has seen the other three rats. Lothor would certainly use a bow to target the giant rats if he is alerted to their presence. But short of that he doesn't know about them.
Also, there appear to be hundreds of rats - death by a thousand paper cuts does not sound like fun. Lothor can crush them one at a time but that doesn't do much good. Anybody have an ability to wipe out large numbers of rats at once?
Speak to animals seems like an option, but . . .
1. Probably only after the mass has been dealt with.
2. It is likely the average little critter knows nothing beyond the object of their search. The 3 big ones on the other hand might know more. The wererat theory seems reasonable.