Constitutionally, "the ticket" has no existance. The electoral votes for President and VP are separate. If you watched the count in Congress, you'd see there were Two counts, two separate sets of ballots. Only if one wants to overturn the actual election, would Biden not be legitimately the VP. Biden is presumably eligible.
Now he might be as guilty of fraud as BO and Pelosi, but that's a separate matter from eligibility, and would have to be taken up by the House in impeachment proceedings. Which they might attempt in order save their sorry selves. Won't work but they might think it would.
Yes, you are correct.
But I wonder if Biden would move up the ranks. If the “candidate” Hussein is found ineligible, then the next largest vote-getter should be declared the winner. Hussein’s swearing in and occupying the oval office is secondary to him not being eligible to be a candidate.