Am aware of the groupings but there's nothing stopping them keeping more than one group
They may look at implementing a similar set up to Dubbo with multiple exhibits.
The medium sized female pod would be their main drawcard - in the largest exhibit; with additional facilities and hippos acting in support of this. Single hippos e.g. a bull won’t bring in additional visitors, so they’ll likely be mindful of that in that additional exhibits will be simple and equipped to hold a small number of hippos.
A starting point could be three (small) additional exhibits - one to hold the bull; the other two to hold cows and their newborns. This will be necessary once there’s adolescent and adult offspring from their previous births in the main pod.