Lots of folks double batt quilts, so I don't think the 2 batts are going to be a problem per se, but were you also planning on each having a backing prior to joining? that might put it over the top. I've used a layer of wool over a layer of w&n.
Not sure how you are going to keep the 2 layers together without some sort of stitching or tying. If there were backings on both, you could possibly use dots, or squares of fusible every so many inches. If there were no backings, however, using fusible between 2 batts would just pull apart. I would think about tying, using your machine to do bar tacks, or maybe add buttons? I also think you might have an issue with binding. Would definitely consider a wider binding.