Welcome!
You can't....Other than through training and environmental management (aka supervision and blockades)....I will post a lot more, because parrots are super complicated and I hope you researched a lot . Same with a human child or pet monkey...Only this one flies (and cutting that off is not kind either)
A grey is a parrot...a parrotlete= both parrots.. ...this is a human toddler that never grows up. They re-homed your last because she was acting like a parrot...that is serious...and yet they got another parrot? "just had to re-home" is like the understatement of a lifetime in terms of how the parrot felt, but I get that you meant no harm (that said, it's a major problem and very hard on the birds)... This is the same thing, all over again...
Ceiling fans should never ever be on if you have a parrot..this is the tip of the ice burg. Please read this thread and all of the links for extreme detail, as you are probably the only one that can help your parents see that what they are thinking is wrong--please see my reply and links
http://www.parrotforums.com/questions-answers/89863-thinking-getting-cockatiel.html <-- I would post all of these same things for you and your parents- so please read my reply, watch the videos and view every link (as well as the links within the links!)
Also-- all parrots are sweet until sexual maturity...prepare for that as well and don't start things now that will be sexual later (no huts, no tents, no full body stroking..,.pet only on the head and neck EVER-- unless medical) 10 hours sleep nightly= essential (and on a schedule)
On Teflon/PTFE/PFOA/PFCs- because your parents sound new to his (make no mistake, any use of these in the same home harms your bird, whether or not you see it)-doesn't matter if the bird is in another room...This is huge.
https://www.ewg.org/research/canaries-kitchen