A single Product neither can have multiple Companies assigned to it nor can it hold multiple Barcodes*.
A product can either be assigned to a single or none (all) Companies. If you have multiple Companies, each one allowed to access a subset of your catalog, you either need to go for customization or create the distinct Product for each Company.
About Barcodes: Please reconsider your approach since the point of using a Barcode is to identify a specific product, thus, different Barcodes => different Products. You could, cover this with Product Variants though (what the differentiating Attribute and Value on these Products would be is up to you) - yet, these would still be different Products. Alternatively, and I would assume that's where this stems from, you could define multiple Supplier Codes for a single Product (under the Purchase-tab of a Product [when the Purchase App is installed]) in case these different 'Barcode' originate from them.
Alternatively, you may set up a custom Barcode Nomenclature (even though, I would not advice you to do so given the limited information at hand) so you could, theoretically at least (depends on what you need them for later on) - or simply comma separate them in your import file.
Also, in general: Create a few Products in Odoo manually and export them to have a relevant example set from which you can work your way to the full catalog.
