Isn't Green Wallet a 2-of-3 multisig where you have 2 of the keys while they have the other one? You can restore it on another wallet or manually sign your transactions if they go down. Here is their FAQ: https://greenaddress.it/en/faq.html
No exactly. They offer 2-of-2 primarily, at least for their implementation with Blockstream. There is 2-of-3 but most would use 2-of-2 because it is what they are offered by default.