My wife and I are newlyweds, we married last December, and we're still trying to straighten out the paperwork for our new home. I've been staying with my wife in her family's home for couple of months. 

My brother-in-law is under 18 years old, let's just call him "Jimmy". I've noticed my father-in-law is not strict at all with Jimmy. I've never heard him scolded Jimmy even though Jimmy stays out late and usually gets home at 11:00PM - 12:00AM. We don't have any idea where he stays during his late nights. Jimmy skips his classes without a reasonable excuse and I've never heard my father-in-law say anything to motivate Jimmy to attend classes even though Jimmy has a very poor academic history (it took him 10 years to complete his primary education, instead of the usual 6).

Another thing I noticed is that when Jimmy asks for something (buy a new phone or shoes) my father-in-law never says no. He also gives Jimmy soda daily, which is not really good for his health. It seems to me that he's spoiling Jimmy too much. I feel that there's supposed to be a reward system to motivate Jimmy to strive harder in school and teach him the value of education. I've never seen Jimmy working on homework assignments, thus I believe he is not serious in his studies though he just reached the secondary education this year.

I'm concerned about Jimmy. I have two younger brothers and we've grown up with our parents putting a strong emphasis on the importance of our education, which motivated us to study hard and do well academically.

Should I just let it pass? I'm afraid that my father-in-law might be offended and think that I'm trying to tell him how to parent his own child.

EDIT:
Sorry if I really missed one point. Yes, we do talk about it with my wife, of course I do open up to her, we've been in a relationship for 8 years before we get married. What I usually ask her "Why your father is too kind? and explained what I noticed..", and she will just respond "because that's what my father is", and if I talked about Jimmy to her. She would usually respond to me "We (with my mother-in-law) already tried to correct Jimmy a lot of times, but it looks like that is what he is.". I really appreciate all the response. Though I might just pre-judge Jimmy's action that would affect his future (that is where my concern is). Glad I have not talk about it yet to my father-in-law,