Great camper can to enjoy Oahu! The campground recommended (Sunfarm and Malaekahana) may not be the best but they are ok.
Sleeping at 4 or even 5 with young kids is possible but the mattress are not as good as what you have at home, especially the one for the top bed that is really thick (maybe 1 inch…).
No problem with the electricity. If you plan to cook a lot, you may be disappointed as the stove is pretty small and there is not that much kitchen accessories. But who care if you want to enjoy the local food trucks !
Bottom line, a very good experience, especially with the kids to discover the island out of the mainstream locations !!