Courts will not remove Biden even if a court declares his victory illegal.
His removal will need to be political.
Impeachment is the only real path even if legally he is declared illegitimate
Quo Warranto would nullify all of Biden’s powers, he wouldn’t be able to get any order carried out and it would extend to Harris.
Pelosi would be next in line temporarily. I believe she would be CINC until the 12th Amendment process was executed.