Incredible post. His sister is at university, her dissertation is in Google Docs - all locked out.
@adamndsmith Please let this be an April 1 joke.
@andreaslindholm @adamndsmith It could be. OP gives the order of events in a comment, saying they each lost access to their accounts one by one, then received an email with the CSAM allegation. How did they receive it, when OP made it clear that they couldnʼt access their Gmail accounts?
@jackyan The notice was probably sent to whatever account is setup as the recovery email for the gmail account, which might not be a gmail and which is separate from the email which is locked out.
@iampytest1 The OP says their recovery emails were on Gmail and they were also locked out of those.
@jackyan oh, than that's weird and a suspicious inconsistency
@iampytest1 The claim about their Proton Mail address getting flagged was also strange. Iʼve never heard of this happening. I think itʼs possible, but it is a bit suspicious.

@jackyan I use Proton and can't recall ever having issues with it being flagged as suspicious, though I haven't ever used it for business or banking.
I also find it weird that their accounts weren't all flagged at once, if I read it correctly, but gradually. Granted I luckily haven't had to deal with this type of issue before (I've been locked out of accounts of course but not for this reason and have never setup my accounts like the OOP).

Its not impossible OOP's story is true but they got some elements wrong or lied about some parts which were embarrassing (or the kid lied about some aspects of what happened).

@iampytest1 I agree, it’s entirely believable and I can see it happening, albeit with some changes in the facts. Errare est humanum so they could have got some info wrong.
One theory in the threads was that the son went from account to account, and as he did so, they each got flagged, but I don’t think it was OP who said that.
Like you I don’t have a set-up like the OP’s—and am very thankful that I don’t!