I would say instead of you making the trade for them without reaching their accounts, you should probably tell them what to do and when to do it, that way you could build some sort of signal group in telegram that they can follow.

You could also put some sort of alert if they are too late they shouldn't react as well, that way if they are there and see you giving a signal they will buy with you and they could sell when you tell them to sell as well, but if they are not there that means they won't make any kind of movement at all as well because they are too late.

This way you are not taking control of anything, which I highly suggest because it is quite important to not take control over their money, even if the website gets hacked or scams they might think you are the cause.