dear G. Joseph,
1. If the Visa expires & u haven't entered, u r back to sq one. U have to start the process all over again. redoing ur meds is not the ans. -bad, pretty bad... not at all recommended.
2. If for any reason u cannot enter by the visa expiry, u must write to CHC, well before it expires, alongwith all supporting docs that explains ur reasonning. the chances r, CHC might ofer u a favourable recourse. -it is the best recommended course of action.
3. All family members may not land in one time. the PA must, to complete the PR procedure. others can land later, but again, before the visa expiry date.
4. Yes, the PA's landing is enough to complete the PR Card formalities.
hope that helps.