Attending a conference where my ex-supervisor and his collaborator are present, should I attend? I have been asked to attend a conference and present from my current employer since this conference is highly focused on my research point. In this conference, my ex-supervisor and his collaborator are going to be present and one will give a lecture. My current employer doesn't know about my story since they did not ask. I am afraid and confused on whether to avoid the places they are going to be in as they have tried to destroy me before and it was very harsh or face my fears and face them without speaking. I am also afraid that they would do badmouthing to my current employer.

What could be the best thing I can do, I am highly interested in to be in, but I am afraid of them and I don't know in case I refused attendance, what kind of accuses I can explain to my current employer ( the project I am working in is cooperation between different university, and each university is going to submit their students for this conference which focused only on my research field).
First of all, I’m sorry to hear that you’re going through this.

I would ignore them in the conference. I don’t know if this motivates you, but going to a conference, doing an amazing job and still shining in my field despite their sabotage attempts would be really satisfying to me. 

On a professional level, if your job requires conference attendance and you categorically refuse for whatever reason, it will not help your career. Don’t let them sabotage you further!