I don’t know on what legal basis the courts could tell consenting adult same-sex couples they’re allowed to marry whomever they love, and then tell consenting adult same-sex or mixed groups of three or more (or for that matter, closely-related consenting adults) “No, you can’t, that’s different.”
The only ‘legal basis’ the state has for determining its definition of marriage is simply whatever judges, pols, or the voting majority happen to think the definition should be at any one time. Any logic or consistency doesn’t enter into it beyond whatever judges, pols, or the voting majority decide they want to use.
Freegards