Simple suggestion, - if you cannot clearly see the glass sheet edges in the final render, substitute a single simple cube for both of them. place the 2d face inside the cube in the same depth ads if behind one sheet previous. It may actually help with the render time. As to the grey lines, check your mapping of the glass texture. Sometimes this happens with the offside faces when you have x top, x front or x side set as mapping. Just a suggestion. Looking forward to the final image.

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