What are the risk of buying a home with in laws?

My wife and I are currently living in her parents house and paying all their bills. $4,200 a month total since they lost their jobs. Well we put in over 100k so far so were looking to buy a two family home with the profits from the sale of their house approx 400k. We would also be taking out a mortgage of approx 400k to buy a more expensive two family home. I have been told that my in laws names must go on mortgage and deed to avoid paying gift tax. How can my wife and I protect ourselves in the future if we have to either sell house? If her parents become sick as they get older and may need medicare? If they want to leave a portion of their house to another sibling? And could we get their names off the deed in the future? Thank you for time