cherrybim, Agreed, regarding the eitza tova to avoid machlocas by being maskum to the other side. My simple observation is that if both sides are agreeable and bending over backwards for the other side (an ideal situation), then the proper derech is to follow the minhugim of the Choson.
Regarding the copying, not everytime the goyim copy our minhugim do we stop the minhug. This is a delicate balance our Chachomim make decisions regarding (and it varies.)
I find the Rosh Yeshivos families having “mixed seating and no mechitzas” quite surprising, thats all. How do the woman dance without a mechitza? (Perhaps the most prominent tznius issue, amongst many in such a situation.)