Is there a way to do composite "-source:" search queries removing both twitter and furaffinity?

Having tried queries like..
artist -source:twi -source:furaffinity
artist -source:twi||furaffinity
artist -source:twi||source:furaffinity
artist -source:twi||-source:furaffinity
artist -source:"twi"||"furaffinity" (and single quotes too)

In the first case, only have the last "-source" was working, aka overwriting the previous one, else it just didn't work. Adding/changing || and &&s here and there to test too.

There's no negative alternation syntax, and you can't combine multiple metatags of the same type nor use metatags with alternation syntax.
You'll just have to use source:twi*furaffinity to search for posts which have Twitter sourced before FA, and then the same search with source:furaffinity*twi for posts which have FA sourced before Twitter.

Well I'm trying to search for posts that were sourced from neither Twitter nor Furaffinity... Not getting one over the other
"-source:" does work for one of the two at a time, at the very least.

Problem is that all posts have only single source, if there's multiple URLs they are simply split on pages with row change.

The search was made in the software in mind that all posts would have only single source, so that's why this kind of search is impossible sadly.

This is partial reason why I really would like to have direct links being inserted in the source so it would be easy to search for sample uploads for example.