"They are right there."
Translation:Ne ovat tuossa.
I believe both 'Ne ovat tuossa' and 'He ovat tuossa' are accepted. But the subject needs to be in the nominative case like he, not the adessive case like heillä.
Adessive heillä literally means 'at/by/on them'. We see it in 'Heillä on kissa', which is translated "They have a cat", but more literally says "At them is a cat."