Hi smallduck, and Twilight871:
As smallduck mentioned the expiry date of your PR visa will be October 5, 2011 which is one year exactly from the date of doing your medicals (which means that the visa itself will not be for 12 months exactly because they will deduct the period of time between doing your medicals, and the date they issue the visa).
The second point as Smallduck said as well: You both can land separately but when doing so, the principal applicant must land first, and then the dependents can land anytime later but before the expiry date of their PR visa which is October 5, 2011 in your case.
Very important notice:
If any of you misses the expiry date of the PR visa (does not land), the visa will be considered canceled, and the entire process is gone which means that they will have to make a new application starting from the zero point again, not only the medicals. Therefore, be careful regarding that point.