When you add your friend to your
MDE tell it you want to link by email. It will send a request to your friend and they will need to go into their MDE account and accept the request. Also add the people they manage and send them the request, they will need to accept. Once this is done you should be able to see their tickets & reservations. If you have trouble doing this you can always call Disney IT and they will help you out.
I regularly book for a group of 8-13 and usually don't have a problem with FPs - may have to adjust times but usually can get what we want. I am online 60 days out at 7am Eastern time and I always have a list made out with the hardest to get at the top and just work my way down the list. As an example: if you want FOP and it is on day 5 of your trip, do that one first and move on to the next hardest FP to get even if it is on a different day. Then you can go back in and fill out your days. I don't split the group unless I absolutely have too cause it makes it harder if you try to modify the FP at a later time.