Was the mosque official's action of expelling unveiled women correct, and is there a sin incurred by the one who brought them to declare their conversion to Islam at the mosque?

If a woman embraces Islam before entering the mosque, it is obligatory to provide her with a legal hijab to enter it, for the hijab is obligatory for a woman in the presence of a non-mahram, and its obligation is emphasized in the mosque. As for before her embracing Islam, she is not required to observe the subsidiary rulings of Sharia. The person in charge of the mosque should be gentle with her so as not to alienate her from Islam, for gentleness adorns a thing and removes its blemishes.