I've got doubles/ triples on my CDL-A, and I, personally, would not ever do this.
If they were both the same TYPE of trailer, maybe. Certainly not with a coach (boxy, can't see around) pulling a bike (small, light, flippable) trailer.
Two coaches, two bikes trailers, even two boats, but not a big'un and a little'un.
You would never know if something bad was going on way back there (flat, flipped, loose bike, etc.).
If they were the same size and type, then you could at least see the sides of the second trailer (and the wheel area too).