Yes, but after they left with Tom. Not before, when it would be risky.
I know they tried to distract the Yeerks by capturing Chapman, and succeeded, but after they sccessfully left with Tom they should have starved the Yeerk.
Instead they basically saved the Yeerk in Tom's head instead of killing it. I stand by my opinion that it was the best time. After they left town, though, not before, when Tom's Yeerk could have gotten some support.
well, after they left with Tom, at Grand G's house, Jake had thought the Yeerk had lost this battle AFTER they left the house. But, to Jake's dismay, Tom tried to kill his father to create an excuse to go home. The same way, after they leave, Tom will still try to find a way, and the Animorphs would not be able to do anything without revealing their identities. I mean, Andalites don't interfere with human families.
Plus, if Tom was suddenly free, then the Yeerks would hunt him down. Worse, they would hunt the rest of the Berenson family... then the rest would be easy. From Jake, going to his best friend Marco and his cousin Rachel. From Rachel to Cassie. Then Ax's and Tobias's places. If one of them was infested, so do the Hok-Bajir lose hope.
So, they had no choice to return everything to normal.