Yes, if the other wife or wives have died.
Other than that, yes if the following fits:
1. It is not illegal in the country or locality where they live;
2. It is not against church practices where they attend church;
3. None of them will be church leaders;
4. If the people involved are in free agreement.
5. They are all Christians.
1. They can move to a different country or simply outside of all countries.
2. They can start their own church, or find a different church that accepts this practice.
3. If they are church leaders, they must resign.
4. They should talk it out among themselves so that they are clear about what this entails.
5. Christians are not supposed to marry outside the religion.
Note, however, that having one wife is often difficult. So, there will always be agitation among a family of more than one wife. Generally speaking, don't do this. Much of the idea of marrying has to do with having a family. Set things up in such a way that the children will be benefited. One wife is best. If other helpers are needed, start a settlement with several couples.