UK Revenue information about Phishing Given what I say later, I promise that's a genuine link btw 
I was on my phone earlier, hence keeping it reasonably brief and my fat fingered typing 
The above link shows how deceptive scammers can be and how easy it is to be taken in.
In addition to what prh has said above I would make sure you tell you parents that if they get any emails urging them to take some form of action regarding any account then there are two things they should do and one definite NO NO.
NO to clicking on any links in emails. It's so easy to click as a reflex action following instructions without thinking it through. Impress upon them that they don't have to take any action that urgently, anything can wait a little while.
Next tell them to insert details into a search engine and see if any scam warnings come up.
Yes hover over the sender's email address as we both advised above, but do be aware that they're not all as transparent as the supposed UK government email that was sent from an AOL address
some of the Revenue warnings in the link I've given are very deceptively formed.
The second thing they should do if they feel they need to take any action on an account is to go to the relevant site by typing the address into their browser so that they follow a link they've found, not one provided in an email, that way they should know where they're navigating to.
They need to remember not to rush anything and not to trust anything unsolicited. They might also want to warn any personal contacts in their address book that their account's been compromised and they may have accidentally exposed friends' email addresses too. Not saying that's the case but it will be erring on the safe side and will also reinforce the lesson for your PILs.
Hope all that helps.