They can vote how they want, but I believe most parties use the whip extensively. So they could be kicked from the party/lose party funding. Crossing the floor secured them money from the new party.

There’s nothing weird about this. There was a string of by-elections, so people cast votes (in those ridings). This is how parliamentary governments work.

I can see complaints about floor-crossing though. That’s an act that didn’t involve the voters.

I don’t think there is an actual definition of European state in any of the EU documents, but I’d be happy to be proven wrong.

The term you’re looking for is “tankies”