I guess your in laws will have to prove that they will return back after visit. Though i am not 100% sure, they getting a tourist visa only based on the paperwork that you might provide, might work against them.

I knew someone who did it like that ages ago and got tourist visa rejected for parents even though sponsorship from this side was good. Plan well. Make sure they put a strong case also, showing property, business, job, etc. The tourist visa will be decided based on that. Good luck.