In the case of a replacement vice president both Senate and House have to confirm. The 25th Amendment requires it.
Confirmation is not required. Either House of Congress can reject the nomination or refuse to vote on it. In 1973 a group of House Democrats tried to convince Speaker Carl Albert to block a vote on Gerald Ford's nomination for VP so if President Nixon was forced out (as he was) Albert would take command. Albert rejected such an idea, but would San Fran Nan?
Also, the Presidential Succession Act of 1947 is Constitutionally dubious at best. If there was a double vacancy, there would be a Constitutional Crisis.