How do we know that the Gurus performed miracles, how do we know that Guru Nanak Dev Ji's handprint is truly in the boulder at Panja sahib.
How do we know Baba Ram Rai performed 72 miracles,
How do we know that Baba Deep Singh Ji was able to carry on living after being beheaded,
how do we know Gurbani can truly cure cancer and lead to "supernatural expereinces".
It can't and does not.....however, faith has a great placebo effect.
All tese people who are referred to as "Bhai Ji's" are claimed to have seen god, how do we know it wasnt a hallucination?
God is in all of us, it is up to us to realise "God". Control and defeat the 5 thieves and realise what is already within you.
I would suggest read about Sikhism from rational sources eg Dr Gopal Singh, Dr I J Singh, Patwant Singh etc. You seem to have got your information from Sakhi's which at best are unreliable, and at worst utter nonsense.