Is there a way to tell that our bitcoin is safe after we put it in a hardware wallet for cold storage after 3 or 5 years?
Yes, you can use, for example, two or three different blockchain explorers to check the balance for your Bitcoin address(es).
Or you can set up a watch-only wallet on any PC or phone - import the Bitcoin-addresses but not the private keys and the wallet cannot spend the money, only monitor. The money will be shown by the wallet as &quot;watch-only&quot; or &quot;non-spendable&quot; (depending on the wallet). It will show you any transactions involving money at that bitcoin-address.