-snip
If you disable 2FA, your wallet would be still a 2 of 3 multi-signature wallet, but with two master private keys.
Of the 2 master private keys, one of them is for my receiving wallet address, is that correct? and the other one is?
Your addresses are hashes of a small computer program called a script. That script outlines a condition for spending coins sent to the corresponding address. The condition states that you have to prove control over 2 out of 3 private keys. The two master private keys can be used to generate 2 out of the 3 private keys behind each address and using those private keys you can generate a digital signature proving control over them.