A.D.
My advise is going to be much different than the advice you're being given! Therapy is NOT always the best thing.
When my daughter was 4, she came home from Christmas visit at her dad's. She had long been potty trained so when she started doing things like wetting her bed, we knew something was up. But being that she was so young and experience with two older children, I knew that it could have been that she was sick among other things. My husband was in college at the time so he kept her and my younger one, (then 3) until it was time for school and he would drop them with my grandma. During this time, he started noticing things like how she would cling to him and would cry if he needed to say just go to the bathroom. We started catching her curled up in a fetal position, hiding under blankets and then, my husband noticed for the first time her masturbating. I hate to use that term for it but essentially that's what it was. I called my ex right away to ask about anything happening to her. He assured me that I was crazy and that it must be something else or something happening somewhere else. During the days with my husband, my daughter began to let out bits and pieces and finally she was drawing pictures with him and let it all out. One of my ex's friends/employees was at his house and had molested her. I was shocked and honestly didn't want to believe it. I didn't want to deal with the reality of something so gross happening to her. It broke my heart and made me sick all at the same time. My ex denied it repeatedly but I took steps including taking her to therapy. DFACS got involved in both counties. My daughter had to talk to a child advocate to give her testimony. The police were involved and my daughter essentially had to undergo a pelvic exam. The guy was arrested but my ex would not cooperate so the guy wasn't prosecuted. Nevermind the fact that a 4 year old recounted a story that included a conversation where her dad said, "Get out of my house and you're fired." She didn't know this guy worked for him so how in the world he wanted to think that she made up "you're fired" boggles my mind. We took her to therapy once a week. My daughter's behaviors escalated and became more frequent. My ex's grandfather is a prominent psychologist in Tennessee so I called him to talk to him about it. He advised against her continuing since it clearly wasn't doing her any good by keeping it on the forefront so to speak. She's now 13 and stopping the therapy was the BEST thing I could have ever done for her. She knows it happened.
Now I'm not saying that this is the best advice for your family but I'm relaying what helped with us. If I were in your shoes, I definitely would not have my daughter around them at all until they're much older, if at all. I also don't know that I would be around them either. I would probably just give my husband my blessing to go on without me but then again, that's just me. Some grudges are worth holding onto.