The CPS are on the air intake side of the engine, on the side of the engine basically just underneath the valve cover flange.
Removal and Installation (2010 SHO manual, but should be same for your Flex)
Both sensors
Remove the Air Cleaner (ACL) outlet pipe and the ACL . For additional information, refer to Section 303-12 .
RH sensor
Position the RH turbocharger intake tube aside. For additional information, refer to Intake Air System Components — Exploded View in Section 303-12 .
LH sensor
Position the LH turbocharger intake tube aside. For additional information, refer to Intake Air System Components — Exploded View in Section 303-12 .
Both sensors
Disconnect the Camshaft Position (CMP) sensor electrical connector.
Remove the bolt and the CMP sensor.
To install, tighten to 10 Nm (89 lb-in).
NOTE: Lubricate the CMP sensor O-ring seal with clean engine oil.
To install, reverse the removal procedure.
Sadly anything Flex EB related is gone from Ford/dealer sites, so I cannot snatch a diagram from there to show the layout ...
https://www.rockauto.com/en/catalog/ford,2014,flex,3.5l+v6+turbocharged,3298524,ignition,camshaft+position+sensor,7192https://www.fordpartsgiant.com/parts/ford-sensor-camshaft-po_bl3z-6b288-a.html?Make=Ford&Model=Flex&Year=2013&Submodel=&Filter=(30734)