The magical problem of exchanging bodies between men and women

According to your description, I guess its secret is as follows:

1. It looks like two boxes, but it is actually four boxes, two red and two yellow. The joint of the two boxes is where the steel plate is inserted.

On the surface, there are two people lying inside, but in fact there are four people in four boxes (I guess it may be two pairs of twins). Two of them (a man and a woman) dressed as you described at the beginning, and the other two people (b men and b women) who were hidden in the box in advance dressed as you described at the end.

3. Then the box starts to turn, and when it is finished, two people (B male and B female) hidden in the box in advance are shown to the audience, while the first two people (a male and a female) have been hidden in the box.

This magic single box can be rolled up for people to lie in. And if the two colors are the same, it is not easy for you to notice whether the order of their placement has changed.

Of course, these are just my guesses. I don't know what they are ...