There is a lot wrong with this question. It sounds more like a fantasy than anything else. Either that, or the person being described is the writer of the question, who doesn't want to be identified.
The woman in question, if we take for one moment that this question is genuine, was easy enough to seduce. It sounds like her ex-boyfriend only needed to click his fingers, and she was there, ready to have sex with him. That was on their first meeting. On the subsequent occasion, she willingly went with him to a cheap hotel, and again had sex with him.
This is the point at which the story starts to become ridiculous. How does the waiter discover that they are not a married couple? How does he know where she is, in order to contact her for blackmail purposes? And why would she agree to meet him for sex unless she actually wants more sexual adventures?
I'm actually surprised that this story doesn't reach a climax with her having sex with the waiter and all his friends, with her every orifice staffed with huge cocks, and gallons of semen filling her mouth, and dripping from her breasts. That would be the usual closing paragraph for such a tale.
She would have to have an extremely intimate relationship with her younger brother if she was going to disclose all this information, together with such details of the things she is doing with this waiter and his friends, and the fact that no condom is being used. If this has been going on for a year, one has to wonder whether she is taking contraception of some kind, as the likelihood of pregnancy would be high.
We are talking about a woman with two children, and a husband. I find it difficult to believe that she could successfully run her household, look after her children and her husband, and find the time for hours and hours of sex with multiple male partners. And this is before you even consider how much time off a waiter in a cheap hotel is likely to have.
On the tiny off chance that this is a genuine plea for help, I can only say that she has dug a huge hole for a self by getting involved in a really sordid ménage. She can continue getting fucked, and in all likelihood, enjoying it. Or she can call the waiter's bluff. In all likelihood, if her husband is much of a man, the waiter would be in serious trouble. If her husband isn't much of a man in the first place, maybe that would explain why she has taken a liking to extramarital fun.
I'm sorry, but I really don't believe that this is a true story. For all the reasons I have written above, and it just sounds like a young guy's masturbatory fantasy to me.
By the way, if you want to fantasise about your sister getting fucked by groups of men, that's fine, as long as it stays only a fantasy that you don't relate to others. Unless of course, she genuinely does like to be fucked by lots of men.