"Er will die Immobilien verkaufen."
Übersetzung:He wants to sell the properties.
As a native English speaker, I generally use real estate to mean either property or properties - it should be usable for either. For example, I might say "Do you own any real estate?" meaning one or more properties.
Also, someone who works in real estate isn't going to sell just a single property and then quit ... that wouldn't make sense!
So I believe "He wants to sell real estate" should be an allowed response; PROVIDED that the intent of the sentence in German is general in nature (not these specific properties, but rather properties in general). Was denken Sie?