A man in the presence of an unwell 90 year old woman who is not dressed properly cannot daven. The likelihood that he will feel any sort of physical attraction is just not there. The fact that this doesn’t make sense to you, or anybody else, doesn’t change anything.
As usual, you are mixing up two completely different Halachos. Ervah (which is NOT Hirhur) and Hirhur (which is not Ervah). Both are not allowed, even without the other.
As for the OP, what I have seen sometimes is three sections: One for Men, one for Women, and one for Shegetzes who want to sit with their spouses. The women can dance in their section, and the men in their own section, and the waiters can take over the middle section during dancing.