I've literally never heard of a person so wilfully desperate to be as reckless with their own health as well as others' like your FIL sounds. HOW?!
When DH and I first moved in with FIL & grand-FIL, I found lots of ways to rationalise their behaviour.
Grand-FIL wasn't born in the UK. He moved here in his 20s without his parents. So growing up as an adult, he didn't have family around to learn from. I'm guessing he picked up weird habits. Now, he's not that social. If he also wasn't social when he moved here, he wouldn't have been able to learn from his peers.
FIL probably picked up weird habits from grand-FIL. He also doesn't have much of a social life, so he probably didn't learn from his peers growing up. English wasn't spoken at home, so that set FIL & grand-FIL (and DH and SIL) apart from their peers even more.
If they've never shocked friends by doing something dangerous, they may not have the sense of how dangerous it really is. If DH and I are the only ones shocked by their treatment of the kids, DH and I are the odd ones out, so our views will be ignored.
None of that is an excuse for their behaviour, just my armchair expert explanation of why they do like they do.
Their learned behaviour might not be totally their fault, but their lack of desire to change and be better - that is their choice and I don't want to deal with it.
Luckily, DH is good at picking up 'normal human' habits from me when he realises how daft some things were growing up.
I bought a cheap £3 Ikea bath towel for a sewing project last week. He said it was nicer than any towel he ever had growing up (
we I bought some nice towels when we got married since his two towels were a decade old
and so tiny!).

I'm sure his family think I'm a fool for spending money on good quality things. Whatevs.
