… clearly the Vulgate and Vijñāneśvara are wrong in their reading here.
If Vijñāneśvara uses ādityaskandagaṇapatīnām, he must have seen a source for skanda in the verse and he must have seen the source between āditya and gaṇapati. Either he was undecided about the reading and tried to accommodate both the readings you discuss or he thought of svāmin as standing, by itself, for skanda.