Speaking as a type 1, if you father is still fairly healthy, he isn't doing bad. I too keep my levels low - HBA1 5.2 ish, but manage it without serious hypo (I test a lot!)
Mars bars aren't ideal - too fatty to be absorbed quickly I find - Lucozade much better. If I need hypo help, someone trying to force me to eat ANYTHING won't work (I dread to think what the neighbours think we are up to , when they hear hubby bellowing "get it in your mouth!!) The kids do a "I'm having a drink - will you have one with me approach, which works much better"
How often does he see a DSN? Maybe aiming for 5mmol/l might be acceptable? and would mean fewer hypos.
Good luck to him, and the family