How does certification of the electoral college work? Who certifies and does it take a majority in Congress to certify the electors etc ?

The legislature of each state decides how the electoral votes are granted. But SOME State and Federal courts always ignore the US constitution so....Your 'guess' IS just as valid as ANYONE'S as to what will happen in this time of - lawless 'judges.'

Each state has that authority for its electors.

The certifications, like the elections, are controlled by the individual states, under the authority of the Secretaries of State.  About the only role the federal government has in national elections is to establish the date, other than enforcing laws that guarantee against discrimination by race &c. 

After the electoral college meets and votes the rest is a formality, "The following December, the electors meet to cast their ballot for the president and vice president. The current vice president (senate president) receives these votes and, on January 6th, reads them to the House of Representatives and the Senate. The candidate with the majority of the votes is sworn in as president on January 20th." - Findlaw.com

The individual states all have their own systems for certifying the results of the election.  This then (in practice) controls who gets selected as electors.  The elector position is MOSTLY ceremonial, though the issue of 'faithless electors' has come up a few times in recent elections.  Alot of states have laws binding them to vote in accordance with the popular vote in their state.

The electors go to congress and vote there.