I know how to bone the various birds needed, and have watched and helped husband make a few turduckens "back in the days".
That said, this is NOT an amateur project. I would VERY strongly ask the butcher to bone the poultry for you.
In fact, I'd opt out of the turducken completely and have then butcher bone out the birds, and then make a salmis out of them. This is a sort of stuffed, rolled poultry roast.
You cut off the wings and drumsticks save them for stock or whatever--same with the giblets.
To make a salmis, all you need do is lay the boned turkey out flat (skin side down). Put a good quantity of dressing on top of this and then lay down the chicken (if you are being fancy, get a capon-much juicier and more tender and well worth the extra cost) add more dressing to the chicken layer and then do the same with the duck and some more dressing.
Now, move the whole flabby mess onto a baking cloth, and roll it up just like you would with a jelly roll. Sew up the "seam" and tie the ends of of the cloth tightly.
Drizzle with a bit of melted butter and roast at 350 degrees until a meat thermometer measures 165 degrees minimum (check several places as the meats cook at slightly different rates.)
You'll want to baste as you go along with this, use more melted butter for that.
Once cooked, weight down to cool (I use a foil covered brick for weighting cooked meats).
Salmis can be served hot or cold. The IMPORTANT thing is that they be either kept hot, or cooled rapidly. The mixture of meats and stuffing is food poisoning waiting to happen if not handled properly.
Believe it or not, this is EASIER than making a turducken if only because you don't have to try to shape the darned thing to look like a bird. It comes out looking like a rolled "bird roast"
If you use spinach in the stuffing, you get a really nice effect when you slice it.
I advise using a butcher to bone the meats as either way you can't tear the skin without ruining the final product and I assure you that you will take several tries to get it right.
Westhof and Dick make excellent boning knives, but you are talking around a hundred dollars for a blade.
Rapala makes a darned good boning knife. It is sold in the sporting goods dept as a "fillet knive" marketed towards the fishing types.
I also recommend that you get a set of "carvers gloves" (high end cooking stores) before attempting this type of project. Greasy hands and slippery meat do not mix at all well with razor sharp knives, even though the sharper a knife is, the safer it is.
While the salmis is cooking, you can get a nice stock going with all the leftovers and use that either as the base for a sauce, or save it for later use.