Yes, diazepam is a benzo, it is the compound that you find in Valium pills. It is safer than Xanax because it has a very long half life, it lasts for days in your system so it allows you to gradually taper without suffering too much distress in every dosage drop and it doesn't cause that much of a interdose wd like Xanax does.
Of course your doctor can switch you from Xanax to diazepam, but here comes the problem: you are doing a very serious amount of Xanax, 12 to 20 mg a day Diazepam is much weaker mg vs mg, like a 2 mg bar of Xanax equals aprox 40 mg of diazepam. So you are taking anywhere from 240 to 400 mg a day. That's an enormous amount that no fucking doctor will prescribe for you to take at home, or so I think.
My advise would be to start tapering the amount of xanax, or even better switch to clonazepam (Klonopin, Rivotril, etc ..), wich is another benzo, as strong as Xanax but long lasting like diazepam. Then you can taper that clonazepam to say 3 mg day, the less obviously the better, and from there you could switch that clonazepam to diazepam for a further, more gradual and forgiving taper.
Whatever you do, remember that any taper has to be slow and smooth, no dramatic drops of dose. You can drop by 10% or so and stay in the new dose for 2 or 3 weeks and then drop another 10%,, stay anorher 2/3 weeks and then repeat. When you reach low doses you can change your drop schedule to a more bareable 5% if you feel that you need to do so.
Hope you get your problem sorted.
Stay safe.