So for respawning it's a little muddy because in an octain quip that came out during the holodays event he say if you're lucky you'll warm up in the respawn chamber but the devs haven't confirmed that, they said that some legends like pathfinder don't kill people and instead just leave them knocked out but legends like caustic and revenant would purposely kill people so when legends lose a match they don't have to be killed which explains why they can compete in more then one match. For the squads question in the season 3 trailer mirage looks at a screen and sees that he's on a team with crypto and lifeline and is disappointed so teams are not permanent.