Before I start want to say I am genuinely canvassing opinion here - have framed as an AIBU but am open to people's thoughts.
PIL's have been considering moving house for some time to somewhere that would be more suited to their later years - they currently live in a fairly remote cottage which needs work.
A house has become available next door to BIL and an idea has been floated that this could be suitable for them. It is way out of the range of what PILs could afford themselves so would involve a 3-way split between PILs/BIL family/ourselves.
We have enough money saved that we could buy 1/3rd of the house from about half our savings. DH was able to save a good chunk of money in a period that he had a lucrative contract and we were living well within our means. Since then we have moved house, doubled our mortgage and I am about to go on maternity leave with our first child. DH is still paid well but finds his job very stressful.
Buying the house for PILs is being pitched as a "good investment". I am happy in principle to help PILs financially but AIBU to see this as potentially a very risky "investment"?