If you are reserving all 7 people at once you should be ok without knowing how to copy.
If you go to modify your fp+, you will get options to replace them all, change, copy or cancel. If you click on copy it will then have you select a person to copy from, followed by selecting who to copy to. It will then think for a minute and spit out your options. Ideally, it will give everybody in the group the FP that you wanted at the times you want. If they are not available, it will give you something else (time or ride). For example, If I want to copy Peter Pan, Pooh and 7DMR for my group 7D will not be available on our dates so it will give me Peter Pan, Pooh and some random other ride. If you click ok it will convert the FP selections of every person in the group to what it just showed. Or you can cancel and leave everybody's choices as they were.
ETA: if one of you has control of both families, it may be easier to reserve for all 7 people at once. If that can't happen, you can still only copy to people you have permission to edit for. So if you do your family and your friend gives you permission after you are done you can try to copy all your FP+'s to them. It may or may not work as described above. If you want to ride together I suggest one of you gives permission and you search for anything hard to get as far out as possible as a whole group. Otherwise things like Anna/Elsa and the mine ride aren't likely to be together from what I've been seeing in my experience just now.