That is impossible to know. Although humans like to claim that humans are the most intelligent animals on the planet the reality is that we have no way of testing this. It is not just intelligence that determines what can be achieved, dolphins could actually be more intelligent than us and just lack the limbs that would enable them to maximise use of that intelligence.

I never believe any statement preceded by "It's a proven fact". However, reading your question I have to wonder if it wouldn't help for you to spend more time in schools, like a dolphin. (Yes, they can be called schools, as well as pods.) I counted seven mistakes that would make your English teacher's hair turn grey.

No, because you are mistaken about the intelligence of dolphins, Brain size and intelligence do not match up, much of the brain of a dolphin is used to process echo location stimuli and not "intelligence".

Probably

no