If I have the correct organization...
From what I can tell so far, it is a branched off church from the Worldwide Church of God founded by Herbert Armstrong...
It seems to have some of the more rigid elements of Seventh Day Adventists and Jehovah's Witness groups in it...
The Living Church of God/ Tomorrow's World splintered off from the WCG after Armstrong died in the 80's. The Tomorrow's World founder, Paul Meredith, began changing many of the core doctrines that were practiced in Armstrong's WCG...
Even though Meredith disagreed with many of the doctrines of Herbert Armstrong and the WCG, he fought for and won the libraries of WCG when the original church splintered and branched. This, he considered as a major victory and claimed that his was the rightful and true descendant of the original WCG...
They general feel that their members should avoid politics, voting, juries, and other civic responsibilities...
They push their members to uphold the Leviticus laws to the letter...
They teach that Europeans are descendants of the lost 10 tribes of Israel...
Avoid most holidays as pagan...
There is much centering on the founders as prophets, and some teaching that Armstrong was a modern day Elisha heralding the end times. I think this is what is most disturbing, because they focus a lot of energy expounding on their founders, and that always sends red flags up for me...
Let me know if any of that sounds familiar, and if you can get any specific information from your father-in-law, post it, and I will try to look deeper. As of right now, I can't find any thing that makes this organization inherently dangerous, but I don't have much specific info to go on. Apparently, there were splinter groups from splinter groups, and some might be much different from the parent organization.