If there's room to centre the mirrors on both sinks then you're ok. I don't know how wide the sinks are. Measure from the centre ( drain) on the sink to the wall and see if it's more than 18" (half of 36"). To see what this is going to look like, get some graph paper and draw it to scale. You might find that a vertically oriented rectangle is the most practical size for your bathroom. If you are looking for something unusual, get a rectangular mirror (vertically oriented) that has an arched top.