Public uprising against established order. Which is a) something any legal system prosecutes, and b) something these people did. There is also in Spain a aggravating case for doing this from a public role, which seems reasonable and also applies to some of these individuals.

Ok, but that's not generally what sedition means

Irrespective of the undertones that you read in the word, that is what they are being judged for. It has a precise technical meaning in the law. And I’d like to know if there is any country whatsoever in which public uprising against the state from a government official, using public funds, and in the manner carried out by them in this case, is not prosecuted.

You have to take into account that this is not a military uprising of a few people, its a pacific protest from politicians who represent almost half of the Catalan votes.

There are plenty of examples where people have been pardoned in Spain for more ethically questionable reasons [1]. This, in contrast, is a clear case where it should be resolved politically, not through the legal system.

[1] https://civio.es/el-indultometro/2013/05/06/saenz/

The political pardon must come after the judicial trial, and comes from different, independent, branches of government.