Converting primary residence into investment overseas

[Sophia Maler]

I own 1/3 of my parents' apartment overseas. My parents (both retirees) still live there, but plan to come to the US and live with me. They don't want to sell the property to the 3rd party now because the prices are going up, and they don't want to be subjects to US tax if they sell it later, when they become permanent residents (right now they are not).

They offered to sell it to me. I'm not sure what to do because I already own 1/3 of it. Right now it is kind of investment for me already. What happen if I buy it for investment purposes? Can I use my self-directed IRA to buy it from them?