"The fact that it was at one time a personal residence or that they are in the military is irrelevant."

I think this is the pertinent detail: "This allows active-duty military members who are away from their property due to PCS orders to extend the 60-month period up to an additional 10 years. This means that eligible military members may exclude their capital gains as long as they occupied the primary residence for two of the previous 15 years."

https://www.militaryonesource.mil/financial-legal/taxes/income-tax-and-rental-properties-when-milita...

"They also sold their main home in another state but I can handle that one. surprise"

Are you aware if the military has a provision which allows more than one primary personal residence exemption for capital gains exclusion in the same tax year? Otherwise, you don't get both.