How to instantiate MultiSigTestnet to create a MultiSig 2 of 3?

[Pep3M]

In the official documentation they do not address the issue of creating a multisignature in depth. For example, they only show these 2 lines of code:
tx_1 = multisig1.create_transaction([('1Archive1n2C579dMsAu3iC6tWzuQJz8dN', 190, 'jpy')])
tx_2 = multisig2.sign_transaction(tx_1)

When we look at the parameters that MultiSigTestnet receives, we see a private key, a list of public keys, and the number of signatures needed. I assume that I get the private key from an instance of PrivateKeyTestnet, but where do I get the list of public keys from?
Ex.
user1_key = PrivateKeyTestnet()
user2_key = PrivateKeyTestnet()
user3_key = PrivateKeyTestnet()
multisig = MultiSigTestnet(user1_key,[user1_key.public_key, user2_key.public_key, user3_key.public_key],2)

I think the above is wrong. I will appreciate any help