Hi Ibrahim,
I'll take, that you are using " map automatically " option, that's why mendix is merging them, bcz it considers them as a single entity.
What you can do is, go to domain model and then create the entity as per your need and then, in the import mapping map them manually by selecting them from the domain model, this way you can get what you intended.
If you cae any problems, just let me know.
Hope it helps!