There need to be at least 3. With two a disagreement cannot be resolved by majority, so the new MCAS will have to disable itself. Pilots will need to be trained to handle this failure mode, and the indicators will need to be added to all the planes (and will need to work, that was an additional issue).
This is a fundamental design flaw for a system which can have catastrophic consequences. This should have been classified as a DO-178B level A system (capable of crashing the plane) but was misclassified by Boeing. DO-178B level A systems require triple redundancy.
This is baloney. There are already 2 AOA sensors on the plane, but MCAS originally only read from one of them: https://arstechnica.com/information-technology/2019/03/boein...