Welcome to our forum. First of all, calm down! There is an "introduction" process that should be gone through before ever allowing two cats to actually face each other. That hasn't happened! Bengals are highly territorial, especially males. Bengals and domestic cats do not always mix. I feel so badly for your little girl. She had her own space, her own home and this other cat comes in and takes over. Bullying is a huge problem and, as you have found out, can cause behavioral issues in your little girl. I do not know that is is best to start the introduction process all over since it is what it is.
First, both of your kitties need their own space. Hopefully, have have a couple of tall cat trees. Your bengal will absolutely LOVE being high up in the air. Second of all, you need separate bathroom spaces for them. Litter box for each and a spare. Unfortunately, that is what a second cat brings to the table.
Next, feed them in different areas so at least your little girl has some peace. At some point, she is going to lose her confidence and your bengal knows exactly what that means -- easy prey. You must NEVER leave them alone together unsupervised. Hopefully, you engage your bengal in heavy play time. They require that. They are not a cat that sleeps 20 hours a day. They need stimulation throughout the day.
You say your family has had bengals. Then you should know what challenges they bring to the table. Bengal/Bengal is fine. Bengal/domestic cat can be problematic!
I don't know that there is anything that is going to calm your bengal down. I would not give medications but you might investigate Jackson Galaxy's Spirit Essences. But ... a bengal is a bengal.
Understand you have two very different cats. The big issue here may be the bengal's earlier life. How he was treated by your family member. What type of stresses he was put under in that environment. Bengals can be difficult to deal with -- I have one of those myself, however, I made a commitment to take care of him his entire life and I will do that, even if it costs me mine!
I suggest you take deep breaths, spend a lot of time with your bengal. Have lots of wand toys and use them. Taking care of a bengal is like taking care of a 2-year old child. They require much more than your regular kitty. Get some advice from your family as well. In the end, you need to protect your little girl. She may never have the confidence to stand up to your bengal. So many bengals end up in rescues because owners simply cannot handle their energy, vocalization, demands. If you understand that's just how a bengal is -- you can't change that -- then you can begin to appreciate and love them for the "wild" cat they are. Hope that helps. We are here for you.