Change your raytrace settings like stwert said and also don't use blinn, with the best will in the world you're not going to get that material looking right. What you need to do with blinn is create fresnel reflections by connecting in two ramps with sampler info nodes to the reflectivity and transparency which is sort of overcomplicating it when you could just render with the mia_material_x in mental ray, fresnel's built in and it looks better.

Look up the fresnel effect, it basically states that reflection changes with the viewing angle so if you fly over the sea you'll be able to look through the water whereas if you stand at the beach light reflects off and it's no longer transparent.

https://www.youtube.com/watch?v=F-2cUWUe0fY

If you look in the manual you'll find some tips on how to set it up;

https://docs.autodesk.com/MENTALRAY/2...ntal-ray-help/
mental ray architectural shader library > quick guide to some common materials

I think your lighting looks quite nice but I'd change all my materials to this one instead, there's a preset for thick glass which would work in your scene. Also check out master zap's blog https://mentalraytips.blogspot.cz/