Yes, he figures it out, that his co-workers are trying to revoke is right to have saying in approval of sale of shares. He figures it out by watching the videos they made of him. In the scene when they play the video of Howard talking to himself he looks at his co-workers, who look down (feeling shame). Also Howard realises they organised people to follow and film him. Secondly they admit doing it and "doing even more".
No, he does not know the real truth and actually his co-workers neither. This questions is partly answered here: Why are Time, Death & Love only visible to Howard?
Hes not disappointed in them. He says that to Whit and emphasises its not over what they did, but because Whit has distanced himself from his daughter and has not taken matters in his own hand to improve the situation. Howard is disappointing, because as he says from his own experience that: "Tomorrow is not promised".
The point of this scene is, that Whit, Claire and Simon realises that Howard is much more informed of their personal affairs and has not forgotten them. They feel shame how they approached to Howard. But also Howard understands he has been off, acknowledges their effort to company and finally agrees that it is right decision to sell shares, which he has been wayward before.