I just inherited 4 properties in Oman with my brothers. I have lived in the US for 30 yrs. And I'm a citizen. One property will generate about 70k in rental income (US dollars) per year. One was just sold for a slight gain. How do I declare properties to US gov't? I also must declare income too, right?

Yes, to both questions.

The sale of the property must be reported on Schedule D, with any profit taxed as a long-term capital gain (probably 5%, but no more than 15%).

The rental income must be reported annually on your tax return using Schedule E, with the building(s) on the property depreciated over 40 years.