Money Moral Dilemma: What's the fairest way to help our children on to the property ladder?

Naomim

We were very lucky my in-laws gifted both MrM and his sister the same amount for a deposit  to get on the housing ladder. 

MrM and I bought an ex council property, overpaid the mortgage and managed to step up a bit to a nicer road and have been here 20 years. SiL and her husband bought a property and were £60k short so "borrowed" the money from the parents.  They since split up SiL struggling to pay mortgage and has avoided repossession by the skin of her teeth. In laws are unlikely to see that money back.

Whilst it hasn't caused any problems between us all, we're a very close family it does irk me that they deliberately chose a property out of their price range and even now treats her Mum & Dad like a bank.