Do all input addresses in a transaction always belong to same user?
Yep, they do belong the the same user(wallet) as far as I know.
Yep. However, you can also verify them here->
https://www.walletexplorer.com/wallet/11e5dada77ed81bc/addresses . You can therefore say that the three addresses(given above) are a part of the same wallet [11e5dada77].