As soon as Jake learned what the stakes were, he should have gotten the Animorphs to help him remove all of Tom's electronic devices (if any) and bar him from using any phones. In an even more ideal situation, Jake would have heard about the trip into the mountains his family would need to take before Tom did, and he'd be able to trap Tom even sooner.
So you cut Tom off from being able to communicate with his "friends". You expedite the trip into the mountains while keeping Tom restrained with handcuffs. Of course "he" (his Yeerk) would constantly complain and yell obscenities, and this would make some sense to Steve and Jean. But if you aggressively contain Tom like this without mercy, his Yeerk would eventually die, and after that, the real Tom would be infinitely thankful, and the Berensons come out of the ordeal much stronger than before; a closer-knit family.*
How would you execute a more aggressive plan for stopping Tom in this situation?
*Of course, this makes me wonder what the Yeerks would do with the Berensons after they got back to the city. Let's discuss that!