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Transferable neural network potentials have shown great promise as an avenue to increase the accuracy and applicability of existing atomistic force fields for organic molecules and inorganic materials. Training sets used to develop transferable potentials are very large, typically millions of examples, and as such, are restricted to relatively inexpensive levels of ab initio theory, such as density functional theory in a double- or triple-zeta quality basis set, which are subject to significant errors. It has been previously demonstrated using transfer learning that a model trained on a large dataset of such inexpensive calculations can be re-trained to reproduce energies of a higher level of theory using a much smaller dataset. Here, we show that more generally, one can use hard parameter sharing to successfully train to multiple levels of theory simultaneously. We demonstrate that simultaneously training to two levels of theory is an alternative to freezing layers in a neural network and re-training. Further, we show that training multiple levels of theory can improve the overall performance of all predictions and that one can transfer knowledge about a chemical domain present in only one of the datasets to all predicted levels of theory. This methodology is one way in which multiple, incompatible datasets can be combined to train a transferable model, increasing the accuracy and domain of applicability of machine learning force fields.