Exactly as the error says: DataFrames and InMemoryDatasets both export a function named groupby, so you have to make clear which one you want by calling either DataFrames.groupby or InMemoryDatasets.
I would advise against using these packages at the same time. DataFrames has been around for a long time and there are a bunch of excellent learning resources, e.g. here for the type of split/apply/combine stuff you’re looking to do: