Seat belts in Michigan?

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I can do an Internet Google or Yahoo search as well as anyone else I assume.  That being said, anyone from Michigan know about current seat-belt regs for sure?  I grew up with no seat-belts and my first set of kids did not even need child-seats.  But as we know, things have changed.   My question relates to my 1988 Toyota Minicruiser.   Two of my kids are coming next week to visit along with my grand-daughter who is 10 years old.  I think we will take a few family trips around northern Michigan and the "real" northern Michigan in the UP.  That means four adults, one 10 year old kid (my grand-daughter), one 12 year old kid (my youngest son) plus a overweight Border Collie.
We have two seat-belts in back for the dinette seats. None for the coach-bed.  As far as I can tell, I'm legal as long as the front passengers have belts, and the two kids at the dinette have belts.  Nobody else in back needs restraints - I think. Just want to make sure.   Last time any of my kids came to visit I was still living in central NY.  I picked up my son at Albany airport (he just got out of the military where he did not wear seat-belts).  We were driving home on the Interstate and a State Trooper pulled us over and gave him a ticket for not wearing a belt.   You'd think a cop being paid likely $75K a year had something more important to do.  One of the reasons why I left NY.  Police are much less common here and the ones that are around tend to be much nicer.  Still - I'd like to avoid problems if possible.