I didn’t ask how it would work. I asked what the grounds for removal would be?
I’m talking about what legal process is used, and what grounds are given for that process.
Of course, it would need a majority in both Houses, and in practical terms would require popular approval too.
What are their grounds for the power they currently wield??
The grounds for the power they currently wield is that it’s the law.
In this case...Constitutional.
Taking away their political powers / their status as royals is one thing, but exiling someone is punishment. You can't just hand out punishment for no good reason.
If they commited crimes that were illegal at the time they were commited they should stand trial for that, but I very much doubt any of those are serious enough to warrant exile.