Genetically all human beings are of the same species, regardless of whether or not they're reproductively fertile -- science looks at populations, not individuals, and no population of humans is reproductively isolated from any other. Your second question is a legal one, not a scientific one. I'm not a lawyer but I seriously doubt you'd have much of a case arguing that infertile people aren't human beings.
I would still like to know how, and if, ring species are 1 specie or 2.