Please read carefully,
In Matthew 18:19, Jesus introduced the prayer of agreement when He said, "Again I say to you that if two of you agree on earth concerning anything that they ask, it will be done for them by My Father in heaven" (NKJV).
Right off the bat you can see that for the prayer of agreement to work, the people involved in the prayer have to agree! You cannot know what someone else wants—what someone is believing for—and God cannot answer your prayer for someone else against his or her will. To use the prayer of agreement, you must be sure that the person with whom you are agreeing is in line with what you are asking for.
If someone asks me to pray in agreement with them, I ask, "What specifically do you want me to pray for?" You absolutely must make sure you are in perfect agreement about what your prayer request is before you join with another believer in the prayer of agreement.