Worried my dad has fallen for a whatsapp investment scam

My dad was contacted through WhatsApp by a group called Doppler Investments. He has been trading with this group for almost 2 months he has lost money and made money. But he has not really transferred off the exchange. They are having him use an exchange called XUSCoins and he is trading cryptos like STE, AAVE, BGV, NEC. He was able to transfer some money off the platform once but it was only $75 about a month ago. I just had him initiate another withdrawal to his trezor but it has not shown up yet. It was USDT or ERC-20 so I don’t know how long that would typically take to show up. He is convinced this is all legitimate but I am really concerned. He has 50k on the platform right now. Are there any telltale signs I should have him look out for to see if this is legitimate?

Update* It seems that he most likely has been scammed. Please be nice my dad is 65 and has stage IV cancer that may be impacting his cognitive function. Can someone ELI5 exactly what steps he should take now to report this? Would there be any use in trying to play along with the scammer to get any other information?

Second Update His withdrawal went through! He was able to get $1000 of it out. Should he messages the scammers first before trying to make a larger withdrawal saying he needs to the money to take out a larger loan? Or should he just try to withdraw without saying anything?