Number 3 has no 'so that'..
It's not about grammar, it's about meaning - 'so that' should be to make something possible, so:
Number 2 should be 'so that his wife doesn't have to' and
Number1 and 4 are totally wrong because thay don't make sense.
'I publish my books online for free so that anyone can read them' and
'I took photos so that we could remember where people were sitting' are correct uses of 'so that'.