Hello,
me and a friend working together in a business which involves crypto currency.
This is the wrong approach, 2 people and one wallet for cryptocurrency, you never know what your friend can do with your coins, anytime.
Last week, he told me that all our USDT + ETH got transferred to another wallet which is obv not ours.
We stored USTD + ETH on myetherwallet.
You stored USDT+ETH on MEW, or you use MEW only as user interface? If you use MEW as main wallet, Trezor is not have anything with this hack. Private keys should be in Trezor, and MEW is just UI.
All BTCs are still were still there tho, only USDT+ETH got stolen.
So if someone is able to hack a cold wallet, i dont really understand why he just stole everything on MEW and not the BTCs.
Fact that BTC is still there only confirms that Trezor is not hacked (seed exposed), you keep ETH on MEW, and your friend has probably become victim of phishing. If someone gets your seed, all coins from Trezor would be stolen, and BTC would be first transferred.