Officiating a "marriage" like that implies and equates support. Period. It is a direct case of bias. They should face impeachment.
If just officiating a marriage implies and equates support, then I wonder what actual involvement in one of those marriages would equate. Impeach everyone but Kagan.
In truth, whether Ginsburg and Kagan officiated over a SSM ceremony before Obergefell was decided is kind of irrelevant. They had their minds made up beforehand, and they were not interested in the facts.
They should all be impeached, and be forced to show that they did nothing more than say what the law is. While an elected Court was not the intent of the Framers, neither was a Court that could nullify legislation and write new legislation without any precedential basis. Which is, essentially, what they did.
And the guy who ought to be grilled the hardest is Anthony Kennedy. Here's a guy who's a professional swing vote who will always decide for the GOP on political questions (Bush v. Gore, Obamacare, Citizens United) but always fall on the liberal side on social issues. A Harry Blackmun without intellectual honesty, seeking to create a lasting legacy for himself.