Maybe my question wasn’t clear. I wasn’t asking if men and women can join together, but if three women can make a zimmun in front of less than three men, when they all ate together, even if the men don’t answer. Thank you again.
The women may do the zimun in front of men. Also, the Mishna Brura (199:18) says in the name of the Shulchan Aruch of the Ba'al Hatanya (Rav Shnior Zaman zt"l), if there were 3 men and 3 women, the women don't have to answer the zimun of the men, but the women may do the zimun amongst themselves. Furthermore, my colleague on this site, Rabbi Sperling has brought the following to my attention which pertains to your question. Rabbi Ya'akov Fuchs in his book "Halichot Bat Yisrael", draws the following conclusion. Since according to the Shulchan Aruch, even if one only drank with 3 others but did not eat, upon hearing "נברך שאכלנו משלו" should say "ברוך שאכלנו משלו ", it follows that if a man hears three women doing zimun, he may answer, if he ate, even though there is no obligation of zimun upon him. In his opinion this is not considered inappropriate as in the case of one man joining two women (which according to the Mishna Brura (199: 12) men cannot join women or vice versa in order to make up the three required for zimun) since the requirement for the zimun was met by the women alone. Rabbi Fuchs stated that Hagaon Rabbi Shlomo Zalman Oirbach zt"l agreed with this conclusion.