2) Also on the web wallet for trezor to send btc I can't change the sending amount by USD instead of by BTC.
1. I read here IOS not yet support by USB cable, See image below which one are supported
2. you can Insert value you send into USD Box
You have to read trezor manual book https://wiki.trezor.io/User_manual
IINM, those cables have to be certified by Apple before they could be used for such purposes. *kaching*