This has been an issue for some time and is well documented. Even the UK Government website mentions it: https://www.gov.uk/guidance/passport...avel-to-europe - "If you renewed your current passport before the previous one expired, extra months may have been added to its expiry date. Any extra months on your passport over 10 years may not count towards the minimum period needed."

If I recall correctly I think the practice of extending passports beyond the 10 year limit has now stopped. My most recent passport was issued in January 2018 and expires in October 2028 so I got 10 years 10 months when I renewed. It should be fine for travelling back to the UK but not for heading anywhere else!

That said, it sounds like a traumatic time for all concerned. Hopefully the tears have all dried and the family are looking forward to being reunited with dad