Re: Conversations you can have with inlaws…
Yes you can make conversation to everyone if you know their interests. 
Like if you know that FIL has a goat for pet you can talk about goats , what goats like and how their milk is so good for health.
Your MIL is fat , you can talk to her about virtues of dieting and give her some tips about dieting.
Your SIL is married with kids , you can talk to her about her evil ILS.
There you go , you can provide hours of entertainment to all the guests and get into their hearts.