Is it permissible to meet with preachers in a place where men and women intermingle, for the the purpose of inviting non-Muslims to Islam, while the majority of attendees are Muslims?

Not every gathering between men and women is considered forbidden if the Shariah controls are met, such as segregation, prevention of temptation (fitna), lowering the gaze, and covering the 'awrat (private parts), especially if it achieves a clear da'wah (preaching/invitational) objective.