Believe the specification.
All chemical batteries will have reduced capacity at higher discharge rates.
I thought the amp-hour rating was high if you specify shorter periods of time.
No, you can draw a higher current for a shorter time but the total energy the battery provides will be lower at higher discharge rates. There will be several reasons for ...
I can see a few issues:
The UltraFire batteries shown in your photo (and in your calculations) are fake. It is impossible to have 12,800 mAh capacity 26650 batteries. This is similar to my answer here about 18650 batteries. The largest capacity 26650 batteries currently available are less than 6000 mAh.
UltraFire BRC26650 7800mAh (Red) - test ...
They can used together, if they're powering different circuits, or different parts of the same circuit.
If you're doing a quick test, they can be put in series with clip leads to power something, but not for long. Do not approach a full discharge. Do not wire them permanently. Do not attempt to charge them. They are a temporary power source, nothing more.