I figured this out mathematically, so I'm not sure if this will be perfect,
but the results I came up with are as follows:
6 cups banana liqueur
6 cups coconut rum
6 cups Myer's Rum
half fill orange juice
half fill pineapple juice
The grenadine is just a guess, but I'd say no more than a cup's worth.
This is based on the following recipe:
1/2 oz. banana liqueur
1/2 oz. coconut rum
1/2 oz. Myer's Rum
half fill orange juice
half fill pineapple juice
float grenadine