There were simultaneous eruptions of Tavurvur and Vulcan (this is discussed in this Wiki link). Importantly, these (and another volcano) all represent different vents that are part of a single system, so it it definitely analogous to the Mauno Loa and Kilauea example in a sense (though I don't know that much about the detail vent system or structure for the Rabaul Caldera and associated vents). Importantly (and as discussed a bit in the Gonnermann paper I linked in the original answer), there is always the potential that if the influx of melt into a magmatic system is significant enough, you can definitely get simultaneous eruptions in adjacent vents (i.e., the mechanism that potentially drives eruption in one or another vent they present can be overwhelmed if there is just a lot of magma).