It is fine to put multiple tables inside a dataset. I tend to group logical items together. For example I would have a customers dataset, and a faults dataset. Thus you mught have a table

Customer
CustomerID
Customer

CustomerDocument
DocumentID
CustomerID
Document

etc

and a faults table

FaultType
FaultTypeID
FaultType

CustomerFaults
FaultID
FaultTypeID
CustomerID

hope this helps!