These three members of the noble gas family all have one property in common because they are gases at room temperature. that is they

The members of 18 group of periodic table like He, Ne, Ar, Kr, Xe, and radon, belongs to the noble gas family. They are compressible, relatively dense and have no definite shape but have definite volume.

definite volume.

Explanation:

The members of the noble gas family like  He, Ne, Ar, Kr, Xe, and radon, all have some in common that is they are colorless or odourless, very unreactive gases and non-metals. They are gases at room temperature. That is they are  compressible, relatively dense and have no definite shape but have definite volume.

Noble gases are the least reactive gases in the periodic table because they have a complete valence shell electrons. These have high ionization enthalpies, low boiling points and negligible electronegativities that's why these are gases at room temperature.        

nucleus

would be most reasonable answer tbh