All 3 are mine, and all 3 have been hired as CoSigners.
The problem here is based on:
If I install an update and that update infects my wallet with malicious code.
I thought that the 2 other wallets would show me the correct address, but the post I read says that all 3 wallets show the same address even if it is wrong.
If I get your question correct you ask of there is exploit on one of the co-signer’s public what will happen to the address, if this I think the address of that wallet will change. It is the combination of all the public keys that actually generate that address so one of them Changing simply means it is not the same again. It is the major reason why you even safe or backup the public keys of other co-signer with your own seed phrase or private key. The wallet is restored with the three public key wallets and as such an exploited public key is different from the original public which means it will create a different address