I've done a lot of shares and everyone here gave you great advice.
1. Prebuy your CD for $99.95
2. Get as many cards you as you want and as many pictures taken as you want-no limits.
3. Don't have the first family enter their codes too soon. You have 30 days to upload your pictures and then another 30 days from then to do your edits. I would wait until both families have returned to upload.
4. You will only have one account-tied to one of yours email. Anyone can access the account that knows the account name (email) and the password.
My tips-
Get as many pictures taken as you can! Tell every PP photog you see that you want as many pictures as they want to take. Ask them to take any special ones they can. Some will only take the requisite 3 but others (who enjoy their job) may take more. On one share I had over 2000 pictures after edits. And that was with only 3 families!
Don't be afraid to act silly! Chances are you will never see the people walking by when you are getting your pix taken. Some of our best are the ones where we were cutting up!
If you are going to either of the waterparks-they have PP photogs there too! We've gotten some great ones there.
Make sure you load pictures from Test Track to your PP card. This is free. I have also heard that Splash Mountain pictures can be downloaded to your card but you have to pay from them.

We ride TT alot so we like to take different photos. For example-asleep, reading a map, acting really, really scared, etc.
Here a just a few of the ones we took last Sept.
Wave pool at Blizzard Beach
DD holding up the "World" (Spaceship Earth)
DD turned 10 on this trip. She's holding up her 10 fingers.
DD and I on an almost deserted Main St. (we had early ADR at Crystal Palace)
DD showing her green teeth after eating a mostly green Snow Ball at BB!
DD on tube in BB wave pool.
DD on zip line at BB
DD doing a splash landing from zip line at BB
DD acting like a lion.
DD holding her baby-Simba!
Playing Air Guitar outide of RnR. This was the one picture that was "lost" the year before. I found out why on this trip. The photographer has to make sure that the Hanes sign is not in the photo. Also I believe there's a trash can that must be blocked out by you and your group as well.
Typhoon Lagoon-we love to get pictures of us getting nailed by the huge wave!
Those are real storm clouds behind us!
I too am doing a share with a few friends in a few weeks. Luckily for me we will be going to DLR after we return from WDW and the CD will only cost $59.95 (plus shipping). The price you pay for your CD is based on the park you are in when your last photo is taken. So I don't need to prebuy this time.
HAVE FUN!