Here's the answer:
“あの二人は、付き合っています”
(ano futari wa tsukia-tte i-masu)
Watch a real native speaker say it:
Here's how it sounds in a textbook:
You could also say:
- あの二人は、付き合ってます
Fun fact: the hundreds of thousands of people learning Japanese with Memrise get this phrase correct 90.73% of the time!
