If the two floating objects turn out to be from the 777, they might be the horizontal stab assembly and the vertical fin. Mass media incorrectly reports the vertical to be 20m / 60 feet. This is the height of the tail above the tarmac parked on the ramp, not the size of the vertical itself. I'd estimate the vertical is 10m / 30 feet which is close to the smaller object.
The horizontal stabilizer is a single assembly made up of the left and right surfaces and the carry-through structure. It's not two surfaces bolted to the sides of the fuselage since it obviously needs to be very robust. A severe g-load (in the air or an impact) that caused a horizontal stab failure would likely separate it as a unit. The span is 24m / 71 feet, again close to the reported dimensions of the larger object.
I'm not sure if the stab contains fuel tanks...if it does, they would presumably be empty and further help with floatation. A 777 expert can clarify/correct this point. Recall the AFA447 vertical was afloat for 5 days with no signs of sinking.
Hope the objects are from the 777 and lead to FDR and CVR.