“Get rid of the old “yeast” by removing this wicked person from among you. Then you will be like a fresh batch of dough made without yeast, which is what you really are. Christ, our Passover Lamb, has been sacrificed for us. So let us celebrate the festival, not with the old bread of wickedness and evil, but with the new bread of sincerity and truth.” (1 Corinthians 5:7-8 NLT)
Paul was writing to the church in Corinth, but he could just as well be talking about any group of people. Even a family.
You know who is not singing from the same page. The one who is only going thought the motions and not really putting their best efforts into it. They will, in time, spread their wickedness and evil until the whole group is poisoned.
So get rid of them. Throw them out, physically or metaphorically. And everyone else will be the better for it.