Financial/legal side of sharing a house with elderly parents

Share your ideas about the practical side of caring.
My sister and brother-in-law are planning to care for our elderly parents by buying a large house for them all to share. But to get somewhere large enough both couples will sell their current houses and contribute to the purchase price.
I am well aware that we need professional legal help on this as the implications are complex (IHT, plus what happens if after all this one of them had to go into a care home etc), but experience has taught me that the so-called professionals don't always understand these areas as well as they should. So -
has anyone out there any informal advice and how do we find a solicitor and/or financial advisor who really knows all the ins and outs?! Many thanks.
I'd try the Carers UK helpline for this one. Details are on this website.

This is such a tricky area because the more people who are involved, the more possible permutations/circumstances that you might need to prepare for.
Thanks Charles - I will do. Image But still interested to hear if anyone reading this thread has done this themselves, or attempted it and given up.