It’s not going to stop with same sex marriage

I've been saying this for years. And get called homophobic for just stating common sense.

WSJ: "If a relationship characterized by love and commitment becomes a Constitutional right to marry, then no state restriction can withstand judicial review. This applies to the number of people eligible to marry, the duration of the contract, and the nature of the individuals eligible to marry (age, degree of genetic relation and so forth). This is not meant as a parade of horribles, but it is a warning that the Court will find itself hearing many cases challenging any state regulation of marriage."

How can you stop 3 sisters and their 10 year old niece from getting married to each other and applying for government benefits if gender doesn't matter, only love and commitment? Why should number matter? Or consanguinity? Or age?