Do editors need all reviewers to be unanimous in their decision before acceptance?
First of all, reviewers give a recommendation. It is the editor who makes the final decision.

It is possible to have an editor going against the reviewers opinion.
An example is this article.
It is open peer-review, so you can read the reviews and the answer of the editor. He says in his comment:


  I decided to continue the review process even though 2 of the 3 reviews recommend rejection.


So the answer is no, an editor does not need to receive unanimous recommendations from the reviewers to make a decision.