Inheritance from abroad from non-US person

My father-in-law who lived abroad and never lived in the US passed away last year and left a substantial inheritance to my wife (above $100K) in bank accounts and properties.
My wife and I are US citizens and file taxes jointly.
My understanding is that we need to declare that inheritance as part of this year's tax report.

My understanding is also that such money is not taxable in the US since her father was not a "US-person" for tax purposes.
Please let me know what the correct way is for declaring that inheritance, which forms need to be used and if Turbo Tax supports such process.
From my research I found form 3520 part IV and form 8938 but it is not clear which one needs to be used or how and when.

Can you help?