Here is what I do when I have a ledger board over siding: The important feature to consider and to properly plan out is the use of angled flashing to fit under the existing siding then to 90 degree out to fit over the ledger, then to 90 down to fit down the front of the ledger. Here the water is channeled down to the ledger then over the ledger and to drip down.
In conjunction with the flashing, I use building paper and even a heavy bead of Butyl rubber caulk. I now have many safeguards to keep the water from getting between the ledger and the siding.
In your situation, the only way I can think of doing this is with your suggestion of a double ledger. But, a double ledger is not as secure as a single ledger. I would still use the flashing steps on the outward sistered ledger.
On the first ledger use lags on every other stud and on the sistered ledger pick up those studs missed, this way a lag won't go into a stud twice and compromise that stud. I would also drill complete pilot holes all the way through down two sizes from the actual dia of the lag. Use washers and then counter sink the first ledger so that the second or sistered ledger will fit snug. Won't hurt to use some HD Liquid nails also on the splice.