According to Blackrock, they haven't bought any single family homes: https://www.blackrock.com/corporate/newsroom/setting-the-record-straight/buying-houses-facts

They do invest in real estate though. They have approximately $60 billion invested in real estate world wide. That's 0.6% of their overall holdings. Taken in isolation, the real estate market worldwide could go to 0 and it would barely affect the value of Blackrock's portfolio.