It's advisable to split it into 3 shipments, but you also need to split it to 3 different names and address if you're shipping it together.

I would however recommend you to get combined version of the generics as that will reduce the amount of bottles needed. But if it is really unavoidable like the previous person (due to lack of combination of the generic), then you'd have to split it. He got the letter of warning is most likely because he didn't provide the prescription letter.

If you can get the doc to confirm if his prescription letter allows you to import 9 bottles, then it's all the better. Just ask the doc to write it clearly the name of the generic, the brand, and the amount of bottles. If it gets stuck in customs, the letter should provide backups and the hospital is responsible for it since they issued it. Although I can't confirm if it works this way since I've never tried it (with this many bottles).

Example:

3x abc (brand x)
3x def (brand x)
3x ghi (brand x)

You can refer to the post above for example of a true copy of prescription letter.