I used bitaddress to generate the bitcoin addresses.
As far as I know, Bitaddress.org is legit. But watch out for many fake sites out there.
I noted that segwitaddress generate the public key without the QR.
I've seen segwitaddress.org before, but I don't know if it can be trusted.
How can I generate the private key alongside with the public key alongside with their QRs as well?
Is there a way to do that ?
I don't know if it exists.
You can manually put something together, starting for instance with the addresses and private keys exported from a new Electrum wallet. I sometimes use command line
qrencode. If you use it offline and air-gapped and verify the QR-codes, you should be safe. But doing that 20 times is pain staking and it's easy to make a mistake.