Helping each other be calm

My husband and I could use some help with learning how to help each other to be more calm while dealing with hard situations with the kids. When one of us isn't being as calm as we should with the kids, sometimes the other will want to remind them to handle it calmly, but won't because we don't want to undermine the other. What would be a constructive, healthy way to handle it if we notice the other isn't handling a situation calmly? We do sometimes offer to take over, which is hopefully a good start…