help solve the problem

[AgVarEs6]

Hi, today I encountered a problem with hacking a telegram account. There, from my account, they sent a circle of my sister, who was not in my gallery. And at the same time, they entered the account without a code and password, I would like to know how this is possible and in this case, was it me or my sister who was hacked because the video was filmed on her camera but sent from my telegram account. And tell me if a data reset will help from my sister's phone so that this hacker would go away forever. A few days earlier my sisters were hacked in the same way, without a code and without a password, it seems that the mail is linked, but the password did not come, but there is the name of his device. If anyone knows what to do, please answer in this topic