You cannot fit 2x 1.8" SSDs since they're physically not 1/2 the size of a 2.5" anyways. You'll run out of room in the first place.
Secondly, the connection for the hard drive allows 1 SATA device, not 2. There are port replication technologies but there aren't any available for a laptop.
Your idea is impressive but it's not possible at this time.