If the house was sold, then that would just give Barb (on her own or by manipulating Chris) a huge chunk of cash.
The best option would probably be to have left the bulk of the estate in a trust to be administered by someone else. They would be charged with dribbling money out as necessary to keep Barb and Chris reasonably comfortable as long as possible. That is a tricky option though. It is a huge slap in the face to Barb. Bob didn't seem to have anyone close enough to do it as a favor. And even if he did, it would be asking them to engage in a decades long unpleasant war with Barb. And the estate was small enough that if he hired a lawyer to do it, the costs of administering it would eat up a substantial chunk of it.