This is reverse passing off, an infringement of the manufacturer's trademark rights. Get permission from the original manufacturer, or don't do it.
Discuss all the details with an attorney in your area.
You face many legal issues, but without knowing the precise items and the extent to which they are protected by trademark law (among others) I cannot begin to advise you. If you relabel someone else's product and pass it off as your own, this can constitute reverse passing off under trademark law both in the U.S. and foreign countries. Further, there may be federal and state regulatory (drugs, safety, health, etc) requirements for the contents of labels which require you to identify the original manufacturer and brand, and various other pieces of information, and failure to include this information on your "relabeled" items could subject you to civil and criminal penalties. You need to retain and work with IP/business/regulatory counsel. Further, you probably will need to obtain a license from the original manufacturer and/or trademark owner before you can do this.