You're on the right track with looking at the camshaft-angle sensor. But rather than the actual sensor itself, the problem is likely to be within the wiring that connects the sensor to the car's computer. Without a good, solid condition, the best sensor in the world can't relay the information that the computer needs to command the engine to start.

The next step is a visit to an auto electrician who should be able to test the cam-sensor circuit and check for problems with fuses, wires, connectors and any other component that could be causing the information breakdown.

The used Captiva does appear to be great value, but their shaky reputation for reliability would lead me to consider other options. The Territory would be a better bet, but they are known to have electrical and front suspension issues in the long-term.  If you're after an SUV, a seven-seat 2006-12 Mitsubishi Outlander is smart buying at the moment, but if you're just after the seven seats, I highly recommend taking a look at a 2008-13 Kia Rondo. These represent excellent value at the moment. Hope that helps, and keep us posted with your progress.