Does a wife's divorce count if the husband jokingly said, "If you don't give birth to ten, then you are divorced"?

Divorce, whether said in jest or earnest, is binding. However, what you discussed with your brothers appears to be an announcement of a future event and a promise to initiate divorce. The condition is tied to someone you might marry in the future, not a condition for divorcing your current wife if she doesn't bear ten children. Therefore, no divorce results from this, and you are not bound by anything. We advise you to avoid using divorce pronouncements, whether in jest or seriously, and to refrain from lying about it, for the Messenger of Allah, peace and blessings be upon him, said: "I guarantee a house in the middle of Paradise for one who abandons lying, even when joking."