I don't have any assistance to give, only that I recently had some FB login trouble myself, and maybe they should contact FB support. They might be required to provide some legal ID (another colleage who had to access a hacked account had to do this)

I only came to say that Facebook engineering seems broken. There does seem to be a lack of quality control in the company, and it shows up in weird edge cases like this.

I expect more threads on this in the future when it becomes harder to ignore.