IMO the situation with the older children is extremely relevant to this case, at least in parts.
When deciding if it’s reasonable for the average parent to think it’s not a good idea to be living in a tent, it helps enormously to know that they were specifically told that it was not safe with their eldest child.
When deciding if it’s reasonable for the average parent to know that it’s not a good idea to co sleep (it’s not cosleeping but for the purpose of this) sitting up not on a safe, firm surface with room around you, it helps enormously to know that they were specifically told that it was not safe to fall asleep holding the older child.
Some parts are likely to have been withheld, and there were many arguments over the ‘agreed facts’ but some is needed to understand the extent of the help and advice that these two were offered, which they neither accepted nor learnt from.