大樂透

雙性人 are called "intersex"

There are some intersex individuals that have abnormal sex chromosome composition, deviating from the norm XX female or XY male. For example, they may be XO, XXX, XXY, XYY, or XO/XY mosaics. All of these chromosomal abnormalities can lead to some degree of intersexuality, where genitalia and/or secondary sexual characteristics are neither exclusively male nor female, or which combine features of the male and female sexes.

HOWEVER, there are also many XX or XY intersex. They seem to have normal sex chromosome composition, but still showing intersexuality. This is because they simply miss key genes involved in sexual determination during development. Genes such as SOX9. So these intersex individuals have normal diploidy chromosomes, but they are missing important genes.

Therefore, in summary, it is a lot more complicated to tell what is the cause of a given intersex individual, and you cannot determine "sex" solely on the presence of the right number of X or Y chromosome.

And in answer to your hypothesis, (xy xx)/2 is not likely (unless you are talking about a chromosomal translocation of a part of the y chromosome to a X chromosome). Neither will these people have a 24th pair of chromosome (that case will likely be lethal).