IN: Which person is they?
The military prepared to go to battle with an Amish colony because they felt threatened.
OUT: The military

IN: Which person is he?
James went to Sully's arcade but he refused to let him in.
OUT: Sully

IN: Which person is they?
Soldiers of the armed forces were slowly being phased out by genetically engineered soldiers because they were created solely for the purpose of excelled warfare.
OUT: genetically engineered soldiers

IN: Which person is they?
The NSA sent their agents in the field to retrieve intelligence, but they were not able to gather the intelligence for them.
OUT:
their agents