I have been at every time of year including March, Easter, June and Christmas. I have never run into a line to actually get the fastpass. There are several FP machines at each FP attraction and its encouraged that one person in your party hold the tickets and get all the FP's.
Yes to your question, you can get a FP for everyone in your party regardless of whether they are riding. You can ride using your FP and will definately have time to re-ride using another member of your party's FP. The FP has a 1 hour return time, you can ride anytime during that hour. This should be plenty of time to ride any ride 2x maybe even more.
You should not have to wait to use the FP just enter the FP line and your good to go. Sometimes you join the standby line for a preshow or at some point but usually your wait is minimal. The only time I have had to wait more than 5-10 minutes with fastpass was at RnRc - for some reason that FP line backs up.
The only ride I have not been able to get a FP for is Test Track, on a busy day they can be gone as early as 1pm.
Decide on your must do rides at each park, hit that park in the morning, get FP's and ride something else while you wait for your ride time to come up.
TJ