For pages like T&C etc. I wouldn't use canonicals. It is perfectly normal that all websites have pages like T&C, privacy policy and so on, and even when the websites aren't owned by the same company, they are usually quite similar. I would simply leave them as they are. You will not be penalised for duplicate content, but Google may choose to show only one of the results in organic search results.
If someone was to google "website 1 terms and conditions", Google should still choose to show the T&C of website 1 as an organic result. If you used canonicals, where website 5 is used as the canonical, you would probably have website 5 shown no matter which T&C a person is trying to find.
For product pages, you should be using different content (product descriptions) to avoid this issue. However, we have the same situation, where we have some products sold across more than one website, but we actually only want one of them to rank, so we have used cross-domain canonicals for those products. It has worked really well for us.