If both exposures were right for the light conditions then isn't what happened exposure-wise only the equivalent of exposing the neg at half box speed which isn't a disaster and can be partially corrected by curtailing development time?

Of course there is no way to "cut out" the other figures and the backgrounds will be mixed up but depending on where the figures are on each neg they may be separate and the whole neg can be cropped to cut out as much as possible of the mixed up backgrounds.

There may be issues but it may be salvageable. A good printing exercise if nothing else