The Magic Plus offers 5 discounted tickets a week for 39 each (two parks), 10 in total.
Not sure what days you will be visiting, but if your visit is not in a weekend/monday that means you can only get 5 tickets.
So if one adult buys the Magic Plus, than you have four people left, which means:
1st day: 1 Magic Plus, 4 discounted tickets, cost 156
2nd day: 1 Magic Plus, 1 discounted tickets, 3 regular tickets (99 each), cost 336
3rd day: 1 Magic Plus, 4 regular tickets, cost 396
Total, without the Magic Plus since you already bought that: 888.
So, without wanting to sound negative, you kinda got it a bit wrong
You might be able to use Magic Flex-annual passes, but that all depends on the exact dates you will be visiting. When are you going?