Oil manufacturers recommend a 5W20 or 5W30 fully synthetic oil for this vehicle. For the record, you’ll need 4,5 litres to perform an oil change, and don’t forget to replace the oil filter at the same time. Putting clean oil through an old, dirty filter makes no sense.

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.

The three cars you name all have merit, none has any major issue to be concerned about and all fit your needs, but you will have to shop around to find them within your age and budget limits.