It can be like when there was the N52 Superman and Post-Crisis Superman coming from different continuities before they kind of sort of combined them in Superman Reborn. Chris Kent can be the Post-Crisis child of Zod to the current universe's child of Zod. And I think they would at least be step-brothers but they're still biologically cousins (or something, I really don't give a shit), so whatever they have going on resulting in them having children would be legal in some states of the US.