Yes, CoinJoining is a good means of improving BTC transaction privacy but I don't know if you're aware that a vulnerability was detected about its service years ago, and in other to prevent issue like this when privacy is the top priority is the reason why i suggested to use of 2-3 privacy service.
Using multisig doesn't do anything to improve your privacy.
Privacy wallet for BTC? To achieve privacy you have to run your own full node and verify everything locally. Let's say you use an spv wallet like Electrum without connecting to your own Electrum server over tor but you use a third party server, your privacy is exposed to the server you connect to.
I'm not talking about the use of SPV wallet and when I said privacy wallet I am referring to Wasabi, Samourai, and Sparrow wallet
Out of the three you listed, only Wasabi provides network privacy by default. Sparrow exposes your IP address and wallet addresses to public Electrum servers, and Samourai exposes your IP address and wallet addresses to their trusted server.